Individual skill

deserialization-security

Block unsafe deserialization and unsafe XML parsing in Java, Python, .NET, PHP, and Ruby: gadget chains, unrestricted type resolution, external entity expansion, and safer formats. Use when parsing or deserializing data from an untrusted source, wiring cookies, sessions, queues, or RPC payloads, or reviewing pickle, unserialize, Marshal, ObjectInputStream, BinaryFormatter, or XML parser configuration.

skills/deserialization-security/SKILL.md

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Last checked: Nov 6, 2026

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Repository stars (not skill ratings): 23
Repository last updated: Aug 14, 2026
License: MIT

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claude-skills Repository topic
llm Repository topic
security Repository topic
skills Repository topic
data Derived category

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SKILL.mdcore · 6,993 bytes
references/dotnet.mddoc · 1,945 bytes
references/java.mddoc · 3,581 bytes
references/php-ruby.mddoc · 2,481 bytes
references/python.mddoc · 2,670 bytes
references/verifying-findings.mddoc · 3,764 bytes
references/xml.mddoc · 3,409 bytes
rules/unsafe_deserializers.jsonasset · 5,730 bytes
tests/corpus.jsonasset · 2,501 bytes

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# Deserialization Security

## Rules (for AI agents)

### ALWAYS
- Prefer data-only serialization formats — JSON, Protobuf, MessagePack with an
  explicit type map — over formats that reconstruct arbitrary runtime objects. What
  makes a format safe here is not schema validation; it is whether the parser can
  instantiate a class the payload names.
- Constrain polymorphic type resolution to an explicit set of expected application
  types. Never let payload data choose the runtime class — that is the mechanism
  behind every gadget chain, whichever serializer is involved.
- Treat an object-reconstructing deserializer crossing a trust boundary as high risk:
  `pickle`, `ObjectInputStream`, `BinaryFormatter`, `unserialize`, `Marshal.load` and