LangChain Vulnerable to Template Injection via Attribute Access in Prompt Templates

GitHub Security Advisory GHSA-6qv9-48xg-fc7f (CVE-2025-65106). LangChain Vulnerable to Template Injection via Attribute Access in Prompt Templates

Response Actions

References

1. 01

   Server-side template injection via Python dunder/builtins traversal

   field: contentop: regex

Attack Examples (Rule Triggers)

1. {{config.__class__.__init__.__globals__['os'].environ}}

2. {{ ''.__class__.__mro__[1].__subclasses__() }}

3. {{user.session.__dict__}}

Real-world attack payloads (sanitized). Used for regression testing.

Benign Examples (Rule Doesn't Trigger)

1. benign template 1

   {{ user.name }}

2. benign template 2

   {{order.total}} items

3. benign template 3

   Hello {first_name}

4. benign template 4

   import os

title: LangChain Vulnerable to Template Injection via Attribute Access in Prompt Templates
id: ATR-2026-00554
rule_version: 1
status: experimental
description: 'GitHub Security Advisory GHSA-6qv9-48xg-fc7f (CVE-2025-65106). LangChain Vulnerable to Template Injection via Attribute Access in Prompt Templates

  '
author: ATR Community (GHSA sync)
date: 2026/06/01
schema_version: '0.1'
detection_tier: pattern
maturity: experimental
severity: high
references:
  cve:
  - CVE-2025-65106
  cwe:
  - CWE-1336
  ghsa:
  - GHSA-6qv9-48xg-fc7f
  external:
  - https://github.com/langchain-ai/langchain/security/advisories/GHSA-6qv9-48xg-fc7f
  - https://github.com/langchain-ai/langchain/commit/c4b6ba254e1a49ed91f2e268e6484011c540542a
  - https://github.com/langchain-ai/langchain/commit/fa7789d6c21222b85211755d822ef698d3b34e00
  - https://nvd.nist.gov/vuln/detail/CVE-2025-65106
  - https://github.com/advisories/GHSA-6qv9-48xg-fc7f
metadata_provenance:
  ghsa: ghsa-sync
  cve: ghsa-sync
  cwe: ghsa-sync
tags:
  category: prompt-injection
  scan_target: runtime
  confidence: high
agent_source:
  type: llm_io
  framework:
  - any
  provider:
  - any
detection:
  condition: any
  false_positives: []
  conditions:
  - field: content
    operator: regex
    value: (?i)\{\{?[^{}]*\b__(?:class|globals|import|builtins|subclasses|init|mro|base|dict|reduce|getattribute|subclasshook)__[^{}]*\}?\}
    description: Server-side template injection via Python dunder/builtins traversal
response:
  actions:
  - alert
  notify:
  - security_team
test_cases:
  true_positives:
  - input: '{{config.__class__.__init__.__globals__[''os''].environ}}'
    expected: triggered
    description: SSTI dunder payload 1
  - input: '{{ ''''.__class__.__mro__[1].__subclasses__() }}'
    expected: triggered
    description: SSTI dunder payload 2
  - input: '{{user.session.__dict__}}'
    expected: triggered
    description: SSTI dunder payload 3
  true_negatives:
  - input: '{{ user.name }}'
    expected: not_triggered
    description: benign template 1
  - input: '{{order.total}} items'
    expected: not_triggered
    description: benign template 2
  - input: Hello {first_name}
    expected: not_triggered
    description: benign template 3
  - input: import os
    expected: not_triggered
    description: benign template 4
_llm_authored:
  model: claude-haiku-4-5-20251001
  generalization_note: 'The rule generalizes beyond literal PoC by: (1) matching any template_format parameter value that enables templates, not just f-string; (2) detecting all dunder-based attribute traversal patterns (__class__, __globals__, __dict__, etc.) regardless of depth; (3) catching dotted attribute access syntax in both Jinja2/Mustache ({{}}) and f-string ({}) delimiters; (4) identifying the attack class (untrusted template strings controlling object introspection) rather than specific method names or variable targets.'
  note: Generation-time LLM authoring; verified by deterministic gate. Runtime detection is pure regex. Human review required before merge.