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SEC005-insecure-deser — Insecure Deserialization

Dimension: Security Default severity: High CWE: CWE-502 OWASP: A08:2021 – Software and Data Integrity Failures Languages: All (Python, JS/TS; Rust skipped — bincode/serde are not unsafe by default) Last reviewed: 2026-05-06

What it detects​

Flags use of insecure deserialization APIs that can execute arbitrary code when fed untrusted input. Detection uses two complementary signals per file:

  1. Import scan — at least one import path contains (case-insensitively) a known insecure-deser module substring:

    LanguageRecognised import substrings
    Pythonpickle, cpickle, marshal, yaml
    JS/TSnode-serialize, serialize-javascript

  2. Source scan — the raw file text is scanned for insecure call-site patterns:

    • pickle.load(, pickle.loads(
    • cPickle.load(, cPickle.loads(
    • marshal.load(, marshal.loads(
    • yaml.load( — suppressed when Loader=yaml.SafeLoader, Loader=SafeLoader, or Loader=yaml.CSafeLoader appears within 120 bytes
    • yaml.unsafe_load(
    • unserialize( — only when node-serialize is imported

If Signal 1 (import) is absent the file is skipped immediately. One finding is emitted per matching call site.

Why it matters​

Deserializing untrusted data with pickle, marshal, or node-serialize allows an attacker to execute arbitrary code on the server. These formats embed executable Python/JS code directly in the serialized byte stream — loading a crafted payload is equivalent to running arbitrary code. OWASP A08:2021 lists insecure deserialization as a top-10 risk.

Configuration​

This rule has no configurable threshold. Disable per project:

[rules.SEC005-insecure-deser]
enabled = false

Examples flagged​

Python — pickle.loads on user-supplied data:

import pickle

def load_user_data(data: bytes):
    return pickle.loads(data)   # flagged: insecure deserialization

Python — yaml.load without a safe loader:

import yaml

def load_config(stream):
    return yaml.load(stream)    # flagged: yaml.load without safe Loader=

JS/TS — node-serialize.unserialize:

import serialize from "node-serialize";

export function loadData(data: string): unknown {
  return serialize.unserialize(data);  // flagged: insecure deserialization
}

Examples not flagged​

Python — yaml.load with a safe loader:

import yaml

def load_config(stream):
    return yaml.load(stream, Loader=yaml.SafeLoader)  # not flagged

Python — json.loads (always safe):

import json

def load_data(s: str):
    return json.loads(s)  # not flagged

Fix guidance​

  • Python: replace pickle.loads with json.loads; replace yaml.load with yaml.safe_load or pass Loader=yaml.SafeLoader.
  • JS/TS: replace node-serialize.unserialize with JSON.parse on validated input.
  • Never deserialize data from untrusted sources using pickle, marshal, or node-serialize regardless of any other validation.

Implementation​

References​