detecting-insecure-deserialization

name	detecting-insecure-deserialization
description	Scan a source tree for unsafe-by-default deserialization APIs: Python pickle.loads / cPickle / shelve / dill, Ruby Marshal.load / YAML.load (pre-3.1 default), Java ObjectInputStream.readObject, PHP unserialize, .NET BinaryFormatter / NetDataContractSerializer, Node.js node-serialize, JavaScript JSON.parse with reviver containing eval. Use when: pre-commit gate on services that accept binary blobs, audit of legacy job-queue code (workers deserializing tasks), post-bug-report when "we accept user-uploaded archives." Threshold: any call to a known-unsafe deserialization API on data that originates from user input, network, file upload, or untrusted storage. Trigger with: "scan deserialization", "pickle audit", "java readObject scan", "yaml.load check".
allowed-tools	["Read","Bash(python3:*)","Glob","Grep"]
disallowed-tools	["Bash(rm:*)","Bash(curl:*)"]
version	3.30.0
author	Jeremy Longshore <[e-mail]>
license	MIT
compatibility	Designed for Claude Code
tags	["security","static-analysis","deserialization","pentest"]

Detecting Insecure Deserialization

Overview

Insecure deserialization (CWE-502, OWASP A08:2021) is the highest- severity injection class in many language stacks because it directly maps to RCE. Pickle, Java serialization, PHP unserialize, and BinaryFormatter all execute object-construction code during deserialization. If that code includes __reduce__ / readObject / __wakeup / OnDeserialization callbacks that the attacker controls, the deserialization step IS code execution.

Most legitimate use cases have safer alternatives (JSON for data, YAML with safe-load, Protocol Buffers, Avro). The remaining cases need explicit type allow-lists and HMAC-signed payloads.

When the skill produces findings

Finding	Severity	Threshold	Affected control
Python pickle.loads(...)	CRITICAL	always (untrusted input)	CWE-502
Python pickle.load(file)	CRITICAL	always	CWE-502
Python dill.loads	CRITICAL	always	CWE-502
Python yaml.load(...) without Loader=	CRITICAL	unsafe legacy default	CWE-502
Python yaml.unsafe_load(...)	CRITICAL	explicit unsafe	CWE-502
Python shelve.open(...)	HIGH	pickle-backed; user-controllable filename	CWE-502
Java ObjectInputStream.readObject()	CRITICAL	always	CWE-502
PHP unserialize($input)	CRITICAL	non-literal input	CWE-502
.NET BinaryFormatter.Deserialize(...)	CRITICAL	deprecated unsafe API	CWE-502
.NET