diff --git a/PROJECTS/beginner/deserialization-gadget-lab/.gitignore b/PROJECTS/beginner/deserialization-gadget-lab/.gitignore
new file mode 100644
index 00000000..2dbe4cb8
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/.gitignore
@@ -0,0 +1,26 @@
+# ©AngelaMos | 2026
+# .gitignore
+
+# Dev-only docs (research / plans / context / handoffs) never ship to the public repo
+docs/
+
+# Agent briefing, local only
+AGENTS.md
+
+# Ruby build + dependency artifacts
+*.gem
+/pkg/
+/tmp/
+/.bundle/
+/vendor/bundle/
+Gemfile.lock
+.rspec_status
+
+# Lab working data
+/payloads/
+/loot/
+*.marshal
+*.bin
+
+# Local env
+.env
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/.rubocop.yml b/PROJECTS/beginner/deserialization-gadget-lab/.rubocop.yml
new file mode 100644
index 00000000..232b5dfc
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/.rubocop.yml
@@ -0,0 +1,39 @@
+# ©AngelaMos | 2026
+# .rubocop.yml
+
+plugins:
+ - rubocop-minitest
+ - rubocop-performance
+ - rubocop-rake
+
+AllCops:
+ NewCops: enable
+ TargetRubyVersion: 3.3
+ Exclude:
+ - "vendor/**/*"
+ - "target/**/*"
+ - "docs/**/*"
+
+Style/Documentation:
+ Enabled: false
+
+Style/FrozenStringLiteralComment:
+ Enabled: false
+
+Metrics/MethodLength:
+ Max: 30
+
+Metrics/AbcSize:
+ Max: 30
+
+Metrics/CyclomaticComplexity:
+ Max: 30
+
+Metrics/PerceivedComplexity:
+ Max: 30
+
+Metrics/ClassLength:
+ Max: 250
+
+Layout/LineLength:
+ Max: 120
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/CHANGELOG.md b/PROJECTS/beginner/deserialization-gadget-lab/CHANGELOG.md
new file mode 100644
index 00000000..d59ef371
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/CHANGELOG.md
@@ -0,0 +1,19 @@
+# Changelog
+
+All notable changes to rube are documented here.
+
+The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+
+- Marshal stream parser that extracts structure, class names, and gadget sinks
+ from a serialized payload without ever calling `Marshal.load`
+- Sink classification along the gated/ungated dispatch axis: `marshal_load` and
+ `_load` are reached through a `respond_to?` check, while `hash`, `eql?`, `<=>`
+ and `[]=` are dispatched blind
+- Stream validation rejecting truncated payloads, unsupported version bytes,
+ unknown type tags, out-of-bounds object links and symlinks, oversized fixnum
+ widths, trailing bytes, and nesting beyond a configurable depth limit
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/Gemfile b/PROJECTS/beginner/deserialization-gadget-lab/Gemfile
new file mode 100644
index 00000000..da97d140
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/Gemfile
@@ -0,0 +1,13 @@
+# ©AngelaMos | 2026
+# Gemfile
+
+source "https://rubygems.org"
+
+gemspec
+
+gem "minitest", "~> 6.0"
+gem "rake", "~> 13.3"
+gem "rubocop", "~> 1.88"
+gem "rubocop-minitest", "~> 0.38"
+gem "rubocop-performance", "~> 1.26"
+gem "rubocop-rake", "~> 0.7"
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/LICENSE b/PROJECTS/beginner/deserialization-gadget-lab/LICENSE
new file mode 100644
index 00000000..0ad25db4
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/LICENSE
@@ -0,0 +1,661 @@
+ GNU AFFERO GENERAL PUBLIC LICENSE
+ Version 3, 19 November 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc.
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+ Preamble
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+contain the covered work, unless you entered into that arrangement,
+or that patent license was granted, prior to 28 March 2007.
+
+ Nothing in this License shall be construed as excluding or limiting
+any implied license or other defenses to infringement that may
+otherwise be available to you under applicable patent law.
+
+ 12. No Surrender of Others' Freedom.
+
+ If conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License. If you cannot convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all. For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
+
+ 13. Remote Network Interaction; Use with the GNU General Public License.
+
+ Notwithstanding any other provision of this License, if you modify the
+Program, your modified version must prominently offer all users
+interacting with it remotely through a computer network (if your version
+supports such interaction) an opportunity to receive the Corresponding
+Source of your version by providing access to the Corresponding Source
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+means of facilitating copying of software. This Corresponding Source
+shall include the Corresponding Source for any work covered by version 3
+of the GNU General Public License that is incorporated pursuant to the
+following paragraph.
+
+ Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU General Public License into a single
+combined work, and to convey the resulting work. The terms of this
+License will continue to apply to the part which is the covered work,
+but the work with which it is combined will remain governed by version
+3 of the GNU General Public License.
+
+ 14. Revised Versions of this License.
+
+ The Free Software Foundation may publish revised and/or new versions of
+the GNU Affero General Public License from time to time. Such new versions
+will be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+ Each version is given a distinguishing version number. If the
+Program specifies that a certain numbered version of the GNU Affero General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation. If the Program does not specify a version number of the
+GNU Affero General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+ If the Program specifies that a proxy can decide which future
+versions of the GNU Affero General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+ Later license versions may give you additional or different
+permissions. However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
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+
+ 15. Disclaimer of Warranty.
+
+ THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
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+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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+IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
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+ 16. Limitation of Liability.
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+ IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
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+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+ 17. Interpretation of Sections 15 and 16.
+
+ If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+ END OF TERMS AND CONDITIONS
+
+ How to Apply These Terms to Your New Programs
+
+ If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+ To do so, attach the following notices to the program. It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+
+ Copyright (C)
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU Affero General Public License as published
+ by the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU Affero General Public License for more details.
+
+ You should have received a copy of the GNU Affero General Public License
+ along with this program. If not, see .
+
+Also add information on how to contact you by electronic and paper mail.
+
+ If your software can interact with users remotely through a computer
+network, you should also make sure that it provides a way for users to
+get its source. For example, if your program is a web application, its
+interface could display a "Source" link that leads users to an archive
+of the code. There are many ways you could offer source, and different
+solutions will be better for different programs; see section 13 for the
+specific requirements.
+
+ You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU AGPL, see
+.
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/README.md b/PROJECTS/beginner/deserialization-gadget-lab/README.md
new file mode 100644
index 00000000..408f87f0
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/README.md
@@ -0,0 +1,79 @@
+# rube
+
+A Ruby object-deserialization security lab.
+
+A gadget chain is a Rube Goldberg machine. One untrusted blob goes in, a dozen
+unrelated standard-library methods knock each other over, and code execution falls out
+the far end. This project builds the machine, then builds the thing that stops it.
+
+## Why this exists
+
+`Marshal.load` on untrusted input is arbitrary code execution. So is `YAML.unsafe_load`,
+`JSON.load` with additions enabled, and `Oj.load` in its default mode. This is not a Ruby
+quirk. It is the same class of bug as Java deserialization, PHP POP chains, and Python
+pickle, and it sits at CWE-502 in the CISA Known Exploited Vulnerabilities catalog with a
+**34.8% known-ransomware rate against a 20.1% baseline** across the catalog as a whole.
+
+Most write-ups on this topic teach the exploit. Fewer teach why the obvious defense does
+not work. This one does both, because the second half is where the actual lesson lives:
+
+**You cannot make `Marshal.load` safe with an allowlist.** The `proc` you pass runs in
+`r_post_proc`, which `marshal.c` invokes *after* `load_funcall(... s_mload ...)`. By the
+time your allowlist sees the object, `marshal_load` has already run. The pattern widely
+copied off Stack Overflow is a post-mortem, not a veto.
+
+**Psych's allowlist genuinely is a veto** — for exactly one reason. It checks the tag
+*before* revival, where Marshal checks the object *after* construction. Identical intent,
+opposite outcome, decided entirely by where the check sits.
+
+## Status
+
+Under construction. What exists and is tested:
+
+- **Marshal stream parser** — parses the binary format, extracts referenced class names
+ and gadget sinks, and validates structure, all without ever calling `Marshal.load`.
+ Rejects truncated streams, unsupported versions, unknown tags, out-of-bounds object
+ links and symlinks, oversized fixnum widths, trailing bytes, and excessive nesting.
+
+Planned: version-compatibility matrix, reflection-based gadget scanner, payload builder,
+a deliberately vulnerable containerized target, and the defensive layer.
+
+## Usage
+
+```ruby
+require "rube"
+
+payload = Marshal.dump(Gem::Requirement.new(">= 0"))
+result = Rube::Marshal::Parser.new(payload).parse
+
+result.class_names
+# => ["Gem::Requirement", "Gem::Version"]
+
+result.sinks.map { |s| "#{s.class_name}##{s.sink_method}" }
+# => ["Gem::Requirement#marshal_load", "Gem::Version#marshal_load"]
+```
+
+Nothing above instantiates a class, calls a constructor, or invokes `Marshal.load`.
+
+## Development
+
+Everything runs in Docker against a pinned Ruby.
+
+```
+just test run the parser suite
+just control run the negative controls
+just check both
+just build build the gem with --strict
+just manifest list exactly what would ship in the .gem
+```
+
+## A note on the object-link index
+
+Ruby's Marshal format documentation states that object links are one-indexed. **They are
+zero-indexed.** A self-referential array dumps as `04 08 5b 06 40 00`, where the trailing
+`00` is a link to the outermost object at index 0. The parser is written against the
+observed bytes, not the documentation.
+
+## License
+
+AGPL-3.0-or-later. See [LICENSE](LICENSE).
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/Rakefile b/PROJECTS/beginner/deserialization-gadget-lab/Rakefile
new file mode 100644
index 00000000..2b78c541
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/Rakefile
@@ -0,0 +1,12 @@
+# ©AngelaMos | 2026
+# Rakefile
+
+require "rake/testtask"
+
+Rake::TestTask.new(:test) do |t|
+ t.libs = %w[lib test]
+ t.test_files = FileList["test/**/*_test.rb"]
+ t.warning = true
+end
+
+task default: :test
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/justfile b/PROJECTS/beginner/deserialization-gadget-lab/justfile
new file mode 100644
index 00000000..cf260a72
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/justfile
@@ -0,0 +1,45 @@
+# ©AngelaMos | 2026
+# justfile
+
+set shell := ["bash", "-uc"]
+
+image := "ruby:4.0-slim"
+vuln_image := "ruby:4.0.2-slim"
+run := "docker run --rm --network none -v $PWD:/app -w /app " + image
+run_ro := "docker run --rm --network none -v $PWD:/app:ro -w /app " + image
+
+default:
+ @just --list
+
+test:
+ {{run_ro}} ruby -Ilib -Itest test/marshal/parser_test.rb
+
+control:
+ {{run_ro}} ruby -Ilib -Itest test/control_check.rb
+
+lint:
+ {{run}} sh -c "gem install --no-document rubocop rubocop-minitest rubocop-performance rubocop-rake >/dev/null 2>&1 && rubocop --force-exclusion"
+
+check: test control
+
+probe:
+ {{run_ro}} ruby /app/test/support/probe.rb
+
+matrix:
+ @bash scripts/version-matrix.sh
+
+build:
+ {{run}} sh -c "gem build --strict rube.gemspec"
+
+manifest:
+ {{run_ro}} ruby -e 'spec = Gem::Specification.load("rube.gemspec"); puts spec.files.sort; puts; puts "#{spec.files.length} files"'
+
+shell:
+ docker run --rm -it --network none -v $PWD:/app -w /app {{image}} bash
+
+pull:
+ docker pull {{image}}
+ docker pull {{vuln_image}}
+
+clean:
+ rm -f *.gem
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/lib/rube.rb b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube.rb
new file mode 100644
index 00000000..337b48c6
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube.rb
@@ -0,0 +1,11 @@
+# ©AngelaMos | 2026
+# rube.rb
+
+require_relative "rube/version"
+require_relative "rube/marshal/constants"
+require_relative "rube/marshal/errors"
+require_relative "rube/marshal/node"
+require_relative "rube/marshal/parser"
+
+module Rube
+end
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/constants.rb b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/constants.rb
new file mode 100644
index 00000000..2d0f1ec9
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/constants.rb
@@ -0,0 +1,63 @@
+# ©AngelaMos | 2026
+# constants.rb
+
+module Rube
+ module Marshal
+ module Constants
+ MAJOR_VERSION = 4
+ MINOR_VERSION = 8
+ HEADER_LENGTH = 2
+
+ TAG_NIL = "0"
+ TAG_TRUE = "T"
+ TAG_FALSE = "F"
+ TAG_FIXNUM = "i"
+ TAG_BIGNUM = "l"
+ TAG_FLOAT = "f"
+ TAG_STRING = '"'
+ TAG_SYMBOL = ":"
+ TAG_SYMLINK = ";"
+ TAG_OBJECT_LINK = "@"
+ TAG_ARRAY = "["
+ TAG_HASH = "{"
+ TAG_HASH_DEFAULT = "}"
+ TAG_REGEXP = "/"
+ TAG_OBJECT = "o"
+ TAG_USERDEF = "u"
+ TAG_USERMARSHAL = "U"
+ TAG_USERCLASS = "C"
+ TAG_EXTENDED = "e"
+ TAG_CLASS = "c"
+ TAG_MODULE = "m"
+ TAG_MODULE_OLD = "M"
+ TAG_STRUCT = "S"
+ TAG_DATA = "d"
+ TAG_IVAR = "I"
+
+ BIGNUM_SIGN_POSITIVE = "+"
+ BIGNUM_SIGN_NEGATIVE = "-"
+ BIGNUM_WORD_BYTES = 2
+
+ FIXNUM_INLINE_OFFSET = 5
+ FIXNUM_MAX_INLINE = 4
+ FIXNUM_MIN_INLINE = -4
+ FIXNUM_MAX_WIDTH = 4
+
+ BYTE_SIGN_THRESHOLD = 128
+ BYTE_MODULUS = 256
+ BITS_PER_BYTE = 8
+
+ DEFAULT_MAX_DEPTH = 256
+
+ SINK_TAGS = [TAG_USERDEF, TAG_USERMARSHAL, TAG_DATA].freeze
+
+ SINK_METHODS = {
+ TAG_USERDEF => "_load",
+ TAG_USERMARSHAL => "marshal_load",
+ TAG_DATA => "_load_data"
+ }.freeze
+
+ GATED_SINK_TAGS = [TAG_USERDEF, TAG_USERMARSHAL].freeze
+ end
+ end
+end
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/errors.rb b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/errors.rb
new file mode 100644
index 00000000..5817ad95
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/errors.rb
@@ -0,0 +1,20 @@
+# ©AngelaMos | 2026
+# errors.rb
+
+module Rube
+ module Marshal
+ class StreamError < StandardError; end
+
+ class TruncatedStreamError < StreamError; end
+
+ class UnsupportedVersionError < StreamError; end
+
+ class UnknownTagError < StreamError; end
+
+ class TrailingBytesError < StreamError; end
+
+ class InvalidLinkError < StreamError; end
+
+ class DepthLimitError < StreamError; end
+ end
+end
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/node.rb b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/node.rb
new file mode 100644
index 00000000..34fa1f03
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/node.rb
@@ -0,0 +1,64 @@
+# ©AngelaMos | 2026
+# node.rb
+
+module Rube
+ module Marshal
+ class Node
+ attr_reader :type, :tag, :children, :instance_variables_map
+ attr_accessor :value, :class_name
+
+ def initialize(type:, tag: nil, value: nil, class_name: nil)
+ @type = type
+ @tag = tag
+ @value = value
+ @class_name = class_name
+ @children = []
+ @instance_variables_map = {}
+ end
+
+ def sink?
+ Constants::SINK_TAGS.include?(tag)
+ end
+
+ def sink_method
+ Constants::SINK_METHODS[tag]
+ end
+
+ def gated?
+ Constants::GATED_SINK_TAGS.include?(tag)
+ end
+
+ def each(&block)
+ return enum_for(:each) unless block
+
+ yield self
+ children.each { |child| child.each(&block) }
+ instance_variables_map.each_value { |child| child.each(&block) }
+ end
+ end
+
+ class Result
+ attr_reader :root
+
+ def initialize(root)
+ @root = root
+ end
+
+ def nodes
+ root.each
+ end
+
+ def class_names
+ nodes.filter_map(&:class_name).uniq
+ end
+
+ def sinks
+ nodes.select(&:sink?)
+ end
+
+ def gated_sinks
+ sinks.select(&:gated?)
+ end
+ end
+ end
+end
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/parser.rb b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/parser.rb
new file mode 100644
index 00000000..1eafff04
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/marshal/parser.rb
@@ -0,0 +1,231 @@
+# ©AngelaMos | 2026
+# parser.rb
+
+module Rube
+ module Marshal
+ class Parser
+ include Constants
+
+ def initialize(source, max_depth: DEFAULT_MAX_DEPTH)
+ @source = source.to_s.dup.force_encoding(Encoding::BINARY)
+ @max_depth = max_depth
+ @position = 0
+ @symbols = []
+ @objects = []
+ end
+
+ def parse
+ read_header
+ root = read_value(1)
+ raise TrailingBytesError, "#{remaining} unread bytes" unless remaining.zero?
+
+ Result.new(root)
+ end
+
+ private
+
+ attr_reader :source, :max_depth, :symbols, :objects
+
+ def remaining
+ source.bytesize - @position
+ end
+
+ def take(count)
+ raise TruncatedStreamError, "wanted #{count} bytes, had #{remaining}" if count > remaining
+
+ slice = source.byteslice(@position, count)
+ @position += count
+ slice
+ end
+
+ def take_byte
+ take(1).unpack1("C")
+ end
+
+ def take_signed_byte
+ byte = take_byte
+ byte >= BYTE_SIGN_THRESHOLD ? byte - BYTE_MODULUS : byte
+ end
+
+ def read_header
+ header = take(HEADER_LENGTH)
+ major, minor = header.unpack("CC")
+ return if major == MAJOR_VERSION && minor <= MINOR_VERSION
+
+ raise UnsupportedVersionError, "stream declares #{major}.#{minor}"
+ end
+
+ def read_fixnum
+ marker = take_signed_byte
+ return 0 if marker.zero?
+ return marker - FIXNUM_INLINE_OFFSET if marker > FIXNUM_MAX_INLINE
+ return marker + FIXNUM_INLINE_OFFSET if marker < FIXNUM_MIN_INLINE
+
+ width = marker.abs
+ raise TruncatedStreamError, "fixnum width #{width}" if width > FIXNUM_MAX_WIDTH
+
+ value = little_endian(take(width))
+ marker.negative? ? value - (1 << (BITS_PER_BYTE * width)) : value
+ end
+
+ def little_endian(bytes)
+ bytes.each_byte.with_index.sum { |byte, index| byte << (BITS_PER_BYTE * index) }
+ end
+
+ def read_counted_bytes
+ take(read_fixnum)
+ end
+
+ def register(node)
+ objects << node
+ node
+ end
+
+ def read_value(depth)
+ raise DepthLimitError, "exceeded depth #{max_depth}" if depth > max_depth
+
+ tag = take(1)
+
+ case tag
+ when TAG_NIL then Node.new(type: :nil, tag: tag)
+ when TAG_TRUE then Node.new(type: :boolean, tag: tag, value: true)
+ when TAG_FALSE then Node.new(type: :boolean, tag: tag, value: false)
+ when TAG_FIXNUM then Node.new(type: :fixnum, tag: tag, value: read_fixnum)
+ when TAG_SYMBOL then read_symbol(tag)
+ when TAG_SYMLINK then read_symlink(tag)
+ when TAG_OBJECT_LINK then read_object_link(tag)
+ when TAG_BIGNUM then register(read_bignum(tag))
+ when TAG_FLOAT then register(read_float(tag))
+ when TAG_STRING then register(read_string(tag))
+ when TAG_REGEXP then register(read_regexp(tag))
+ when TAG_ARRAY then read_array(tag, depth)
+ when TAG_HASH, TAG_HASH_DEFAULT then read_hash(tag, depth)
+ when TAG_IVAR then read_ivar(tag, depth)
+ when TAG_OBJECT then read_object(tag, depth)
+ when TAG_STRUCT then read_struct(tag, depth)
+ when TAG_USERDEF then register(read_userdef(tag))
+ when TAG_USERMARSHAL then read_usermarshal(tag, depth)
+ when TAG_DATA then read_wrapped(tag, :data, depth)
+ when TAG_USERCLASS then read_wrapped(tag, :user_class, depth)
+ when TAG_EXTENDED then read_wrapped(tag, :extended, depth)
+ when TAG_CLASS then register(read_named(tag, :class))
+ when TAG_MODULE, TAG_MODULE_OLD then register(read_named(tag, :module))
+ else raise UnknownTagError, "byte #{tag.unpack1('C')} at offset #{@position - 1}"
+ end
+ end
+
+ def read_symbol(tag)
+ node = Node.new(type: :symbol, tag: tag, value: read_counted_bytes.to_sym)
+ symbols << node.value
+ node
+ end
+
+ def read_symlink(tag)
+ index = read_fixnum
+ raise InvalidLinkError, "symlink #{index} of #{symbols.length}" unless symbols[index] && index >= 0
+
+ Node.new(type: :symlink, tag: tag, value: symbols[index])
+ end
+
+ def read_object_link(tag)
+ index = read_fixnum
+ raise InvalidLinkError, "object link #{index} of #{objects.length}" unless objects[index] && index >= 0
+
+ Node.new(type: :object_link, tag: tag, value: index)
+ end
+
+ def read_bignum(tag)
+ negative = take(1) == BIGNUM_SIGN_NEGATIVE
+ magnitude = little_endian(take(read_fixnum * BIGNUM_WORD_BYTES))
+ Node.new(type: :bignum, tag: tag, value: negative ? -magnitude : magnitude)
+ end
+
+ def read_float(tag)
+ Node.new(type: :float, tag: tag, value: Float(read_counted_bytes))
+ rescue ArgumentError
+ Node.new(type: :float, tag: tag)
+ end
+
+ def read_string(tag)
+ Node.new(type: :string, tag: tag, value: read_counted_bytes)
+ end
+
+ def read_regexp(tag)
+ node = Node.new(type: :regexp, tag: tag, value: read_counted_bytes)
+ take(1)
+ node
+ end
+
+ def read_array(tag, depth)
+ node = register(Node.new(type: :array, tag: tag))
+ read_fixnum.times { node.children << read_value(depth + 1) }
+ node
+ end
+
+ def read_hash(tag, depth)
+ node = register(Node.new(type: :hash, tag: tag))
+ read_fixnum.times { node.children << read_pair(depth) }
+ node.children << read_value(depth + 1) if tag == TAG_HASH_DEFAULT
+ node
+ end
+
+ def read_pair(depth)
+ pair = Node.new(type: :pair)
+ pair.children << read_value(depth + 1)
+ pair.children << read_value(depth + 1)
+ pair
+ end
+
+ def read_ivar(tag, depth)
+ inner = read_value(depth)
+ read_fixnum.times do
+ name = read_value(depth + 1)
+ inner.instance_variables_map[name.value] = read_value(depth + 1)
+ end
+ inner
+ end
+
+ def read_object(tag, depth)
+ node = register(Node.new(type: :object, tag: tag))
+ node.class_name = read_value(depth + 1).value.to_s
+ read_fixnum.times do
+ name = read_value(depth + 1)
+ node.instance_variables_map[name.value] = read_value(depth + 1)
+ end
+ node
+ end
+
+ def read_struct(tag, depth)
+ node = register(Node.new(type: :struct, tag: tag))
+ node.class_name = read_value(depth + 1).value.to_s
+ read_fixnum.times { node.children << read_pair(depth) }
+ node
+ end
+
+ def read_userdef(tag)
+ node = Node.new(type: :userdef, tag: tag)
+ node.class_name = read_value(1).value.to_s
+ node.value = read_counted_bytes
+ node
+ end
+
+ def read_usermarshal(tag, depth)
+ node = register(Node.new(type: :usermarshal, tag: tag))
+ node.class_name = read_value(depth + 1).value.to_s
+ node.children << read_value(depth + 1)
+ node
+ end
+
+ def read_wrapped(tag, type, depth)
+ node = register(Node.new(type: type, tag: tag))
+ node.class_name = read_value(depth + 1).value.to_s
+ node.children << read_value(depth + 1)
+ node
+ end
+
+ def read_named(tag, type)
+ Node.new(type: type, tag: tag, class_name: read_counted_bytes)
+ end
+ end
+ end
+end
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/version.rb b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/version.rb
new file mode 100644
index 00000000..2af11c23
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/lib/rube/version.rb
@@ -0,0 +1,6 @@
+# ©AngelaMos | 2026
+# version.rb
+
+module Rube
+ VERSION = "0.1.0"
+end
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/rube.gemspec b/PROJECTS/beginner/deserialization-gadget-lab/rube.gemspec
new file mode 100644
index 00000000..35c2b86d
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/rube.gemspec
@@ -0,0 +1,37 @@
+# ©AngelaMos | 2026
+# rube.gemspec
+
+require_relative "lib/rube/version"
+
+Gem::Specification.new do |spec|
+ spec.name = "rube"
+ spec.version = Rube::VERSION
+ spec.authors = ["Carter Perez"]
+ spec.email = ["carterperez2222@gmail.com"]
+
+ spec.summary = "Ruby object-deserialization security lab: inspect, understand, and defend against gadget chains"
+ spec.description = "rube parses Ruby Marshal streams without deserializing them, discovers gadget " \
+ "sinks by runtime reflection, and ships the defenses that stop them. Built as a " \
+ "teaching artifact for the deserialization vulnerability class."
+ spec.homepage = "https://github.com/CarterPerez-dev/Cybersecurity-Projects"
+ spec.license = "AGPL-3.0-or-later"
+
+ spec.required_ruby_version = ">= 3.3"
+
+ spec.metadata = {
+ "source_code_uri" => "#{spec.homepage}/tree/main/PROJECTS/beginner/deserialization-gadget-lab",
+ "bug_tracker_uri" => "#{spec.homepage}/issues",
+ "changelog_uri" => "#{spec.homepage}/blob/main/PROJECTS/beginner/deserialization-gadget-lab/CHANGELOG.md",
+ "documentation_uri" => "#{spec.homepage}/tree/main/PROJECTS/beginner/deserialization-gadget-lab/learn",
+ "rubygems_mfa_required" => "true"
+ }
+
+ spec.files = Dir[
+ "lib/**/*.rb",
+ "README.md",
+ "CHANGELOG.md",
+ "LICENSE"
+ ]
+
+ spec.require_paths = ["lib"]
+end
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/test/control_check.rb b/PROJECTS/beginner/deserialization-gadget-lab/test/control_check.rb
new file mode 100644
index 00000000..409e3f41
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/test/control_check.rb
@@ -0,0 +1,78 @@
+# ©AngelaMos | 2026
+# control_check.rb
+
+require_relative "test_helper"
+
+Pair = Struct.new(:x, :y)
+
+puts "=== control 1: does the TracePoint oracle actually fire on a real Marshal.load ==="
+fired = false
+tracer = TracePoint.new(:call, :c_call) do |tp|
+ fired = true if tp.method_id == :load && tp.self.equal?(Marshal)
+end
+tracer.enable { Marshal.load(Marshal.dump([1, 2])) }
+puts fired ? " FIRED - oracle is live, the never-calls-load test is meaningful" : " DID NOT FIRE - oracle is broken, that test proves nothing"
+
+puts
+puts "=== control 2: object link index actually present in the stream ==="
+cyclic = []
+cyclic << cyclic
+blob = Marshal.dump(cyclic)
+puts " bytes: #{blob.bytes.map { |b| format('%02x', b) }.join(' ')}"
+puts " ascii: #{blob.inspect}"
+link = Rube::Marshal::Parser.new(blob).parse.root.children.first
+puts " parsed link index: #{link.value} (must be 0, docs claim 1)"
+
+puts
+puts "=== control 3: broad corpus round-trip, parser vs Marshal ground truth ==="
+shared = "shared"
+aliased = [shared, shared]
+cyclic_hash = {}
+cyclic_hash[:self] = cyclic_hash
+deep = [1]
+20.times { deep = [deep] }
+
+corpus = [
+ nil, true, false,
+ 0, 1, -1, 122, 123, -123, -124, 255, -256, 65_536, -65_536,
+ 1_073_741_823, -1_073_741_824, 2**70, -(2**70), 2**200,
+ 0.0, -0.0, 3.14, Float::INFINITY, -Float::INFINITY,
+ "", "str", "\x00\xff binary".b, "unicode é中",
+ :sym, :"with spaces", :marshal_load,
+ [], {}, [1, [2, [3, [4]]]], { a: { b: { c: 1 } } },
+ (1..5).to_a, Pair.new(1, 2), Pair.new(nil, [1, 2]),
+ Object.new, Time.now, /regex/i, //mx, String, Comparable, Rube,
+ aliased, cyclic_hash, deep,
+ { "mixed" => [1, :two, 3.0, nil, true] },
+ Hash.new(0).tap { |h| h[:k] = 1 },
+ Gem::Requirement.new(">= 0"), Gem::Version.new("1.2.3")
+]
+ok = 0
+corpus.each do |item|
+ blob = Marshal.dump(item)
+ result = Rube::Marshal::Parser.new(blob).parse
+ raise "no root for #{item.inspect}" unless result.root
+
+ ok += 1
+rescue StandardError => e
+ puts " FAIL #{item.class}: #{e.class}: #{e.message}"
+end
+puts " #{ok}/#{corpus.length} parsed without Marshal.load"
+
+puts
+puts "=== control 4: mutation - break the link bounds check, does a test catch it ==="
+puts " (verified manually below by feeding an out-of-range link)"
+begin
+ Rube::Marshal::Parser.new("\x04\x08[\x06@\x63").parse
+ puts " NOT CAUGHT - bounds check is dead"
+rescue Rube::Marshal::InvalidLinkError => e
+ puts " CAUGHT: #{e.message}"
+end
+
+puts
+puts "=== control 5: real gadget-shaped payload, class names extracted, nothing built ==="
+payload = Marshal.dump(Gem::Requirement.new(">= 0"))
+result = Rube::Marshal::Parser.new(payload).parse
+puts " classes: #{result.class_names.inspect}"
+puts " sinks: #{result.sinks.map { |s| "#{s.class_name}##{s.sink_method}" }.inspect}"
+puts " gated: #{result.gated_sinks.map(&:class_name).inspect}"
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/test/marshal/parser_test.rb b/PROJECTS/beginner/deserialization-gadget-lab/test/marshal/parser_test.rb
new file mode 100644
index 00000000..4ce6c90f
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/test/marshal/parser_test.rb
@@ -0,0 +1,227 @@
+# ©AngelaMos | 2026
+# parser_test.rb
+
+require_relative "../test_helper"
+
+module Rube
+ module Marshal
+ class ParserTest < Minitest::Test
+ def parse(blob)
+ Parser.new(blob).parse
+ end
+
+ def roundtrip(object)
+ parse(::Marshal.dump(object)).root
+ end
+
+ def test_rejects_empty_stream
+ assert_raises(TruncatedStreamError) { parse("") }
+ end
+
+ def test_rejects_header_only
+ assert_raises(TruncatedStreamError) { parse("\x04\x08") }
+ end
+
+ def test_rejects_wrong_major_version
+ assert_raises(UnsupportedVersionError) { parse("\x05\x08\x30") }
+ end
+
+ def test_rejects_future_minor_version
+ assert_raises(UnsupportedVersionError) { parse("\x04\x09\x30") }
+ end
+
+ def test_accepts_older_minor_version
+ assert_equal :nil, parse("\x04\x07\x30").root.type
+ end
+
+ def test_rejects_unknown_tag
+ assert_raises(UnknownTagError) { parse("\x04\x08\x00") }
+ end
+
+ def test_rejects_trailing_bytes
+ assert_raises(TrailingBytesError) { parse(::Marshal.dump(nil) + "junk") }
+ end
+
+ def test_parses_nil
+ assert_equal :nil, roundtrip(nil).type
+ end
+
+ def test_parses_booleans
+ assert_equal true, roundtrip(true).value
+ assert_equal false, roundtrip(false).value
+ end
+
+ def test_parses_fixnum_across_every_encoding_width
+ [0, 1, 5, 122, 123, 255, 256, 65_535, 65_536, 1_073_741_823,
+ -1, -123, -124, -256, -65_536, -1_073_741_824].each do |n|
+ assert_equal n, roundtrip(n).value, "fixnum #{n} did not round-trip"
+ end
+ end
+
+ def test_parses_bignum_both_signs
+ [2**64, -(2**64), 2**128 + 7].each do |n|
+ assert_equal n, roundtrip(n).value, "bignum #{n} did not round-trip"
+ end
+ end
+
+ def test_parses_float
+ assert_in_delta 3.5, roundtrip(3.5).value, 0.0
+ end
+
+ def test_parses_symbol
+ assert_equal :marshal_load, roundtrip(:marshal_load).value
+ end
+
+ def test_parses_string_through_ivar_wrapper
+ node = roundtrip("hello")
+ assert_equal :string, node.type
+ assert_equal "hello", node.value
+ end
+
+ def test_parses_array
+ node = roundtrip([1, 2, 3])
+ assert_equal :array, node.type
+ assert_equal [1, 2, 3], node.children.map(&:value)
+ end
+
+ def test_parses_nested_array
+ node = roundtrip([1, [2, [3]]])
+ assert_equal 3, node.children.last.children.last.children.first.value
+ end
+
+ def test_parses_hash
+ node = roundtrip({ a: 1 })
+ assert_equal :hash, node.type
+ assert_equal 1, node.children.length
+ end
+
+ def test_object_links_are_zero_indexed
+ cyclic = []
+ cyclic << cyclic
+ node = roundtrip(cyclic)
+ link = node.children.first
+ assert_equal :object_link, link.type
+ assert_equal 0, link.value
+ end
+
+ def test_rejects_out_of_bounds_object_link
+ assert_raises(InvalidLinkError) { parse("\x04\x08@\x0a") }
+ end
+
+ def test_rejects_out_of_bounds_symlink
+ assert_raises(InvalidLinkError) { parse("\x04\x08;\x0a") }
+ end
+
+ def test_resolves_symlink_to_prior_symbol
+ node = roundtrip([:same, :same])
+ assert_equal :symlink, node.children.last.type
+ assert_equal :same, node.children.last.value
+ end
+
+ def test_extracts_class_name_from_plain_object
+ blob = ::Marshal.dump(Fixture.new)
+ result = parse(blob)
+ assert_includes result.class_names, "Rube::Marshal::ParserTest::Fixture"
+ end
+
+ def test_extracts_class_name_without_instantiating
+ refute Fixture.instantiated, "parser must not construct the class"
+ parse(::Marshal.dump(Fixture.new))
+ refute Fixture.instantiated, "parser instantiated a class during parse"
+ end
+
+ def test_flags_usermarshal_as_sink
+ result = parse(::Marshal.dump(UserMarshalFixture.new))
+ sink = result.sinks.first
+ refute_nil sink
+ assert_equal "marshal_load", sink.sink_method
+ assert_equal "Rube::Marshal::ParserTest::UserMarshalFixture", sink.class_name
+ end
+
+ def test_flags_userdef_as_sink
+ result = parse(::Marshal.dump(UserDefFixture.new))
+ assert_equal "_load", result.sinks.first.sink_method
+ end
+
+ def test_clean_payload_reports_no_sinks
+ assert_empty parse(::Marshal.dump([1, "two", :three, { a: 1 }])).sinks
+ end
+
+ def test_rejects_truncated_string_body
+ assert_raises(TruncatedStreamError) { parse("\x04\x08\"\x0aab") }
+ end
+
+ def test_rejects_truncated_array_elements
+ assert_raises(TruncatedStreamError) { parse("\x04\x08[\x08i\x06") }
+ end
+
+ def test_rejects_truncated_multibyte_fixnum
+ assert_raises(TruncatedStreamError) { parse("\x04\x08i\x03\x01") }
+ end
+
+ def test_rejects_depth_beyond_limit
+ deep = "\x04\x08" + ("[\x06" * (Constants::DEFAULT_MAX_DEPTH + 5)) + "0"
+ assert_raises(DepthLimitError) { parse(deep) }
+ end
+
+ def test_honours_custom_depth_limit
+ blob = ::Marshal.dump([[[1]]])
+ assert_raises(DepthLimitError) { Parser.new(blob, max_depth: 2).parse }
+ end
+
+ def load_watcher
+ fired = false
+ tracer = TracePoint.new(:call, :c_call) do |tp|
+ fired = true if tp.method_id == :load && tp.self.equal?(::Marshal)
+ end
+ tracer.enable { yield }
+ fired
+ end
+
+ def test_load_watcher_oracle_is_live
+ assert load_watcher { ::Marshal.load(::Marshal.dump([1, 2])) },
+ "oracle failed to observe a real Marshal.load, so the next test would pass vacuously"
+ end
+
+ def test_never_calls_marshal_load
+ blob = ::Marshal.dump(UserMarshalFixture.new)
+ refute load_watcher { parse(blob) }, "parser invoked Marshal.load"
+ end
+
+ def test_never_calls_marshal_load_on_gadget_shaped_payload
+ blob = ::Marshal.dump(Gem::Requirement.new(">= 0"))
+ refute load_watcher { parse(blob) }, "parser invoked Marshal.load"
+ end
+
+ class Fixture
+ @instantiated = false
+
+ class << self
+ attr_accessor :instantiated
+ end
+
+ def initialize
+ @marker = "value"
+ end
+ end
+
+ class UserMarshalFixture
+ def marshal_dump
+ ["payload"]
+ end
+
+ def marshal_load(data); end
+ end
+
+ class UserDefFixture
+ def _dump(_depth)
+ "opaque"
+ end
+
+ def self._load(_data)
+ new
+ end
+ end
+ end
+ end
+end
diff --git a/PROJECTS/beginner/deserialization-gadget-lab/test/test_helper.rb b/PROJECTS/beginner/deserialization-gadget-lab/test/test_helper.rb
new file mode 100644
index 00000000..bdefdac0
--- /dev/null
+++ b/PROJECTS/beginner/deserialization-gadget-lab/test/test_helper.rb
@@ -0,0 +1,7 @@
+# ©AngelaMos | 2026
+# test_helper.rb
+
+$LOAD_PATH.unshift(File.expand_path("../lib", __dir__))
+
+require "minitest/autorun"
+require "rube"