PT-2026-81115 · Pypi · Mcp-Contextforge-Gateway

CVE-2026-53710

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Publicado

2026-08-24

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Atualizado

2026-09-10

CVSS v3.1

10

Crítica

VetorAV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Commit: f855e54d5b7bc1c91b977574a03b91eff6b86bb6 Component: mcp-servers/python/python sandbox server/src/python sandbox server/server fastmcp.py

Vulnerability

RestrictedPython's sandbox in ContextForge's python sandbox server sub-project allows arbitrary Python execution via three compounding weaknesses:
  1. Raw getattr is exposed in safe builtins, bypassing getattr mediation.
  2. validate code checks for literal dangerous dunder strings, but the payload constructs those names at runtime.
  3. The execute code MCP tool can be exposed over HTTP/SSE transport with no authentication layer.

Proof of Concept

The local PoC was executed against the real pinned sandbox code path. It constructs dunder names at runtime, walks Python's class hierarchy through the exposed getattr, finds subprocess.Popen, and executes a harmless marker command.
Transcript excerpt:
text
POC: IBM/mcp-context-forge RestrictedPython getattr sandbox bypass
validation={'valid': True, 'message': 'Code passed validation', 'warnings': None}
success=True
stdout="FOUND POPEN
b'IBM SANDBOX POC PASS'
"
IBM RESTRICTEDPYTHON GETATTR POPEN REPRO PASS
PoC artifact hashes:
text
beb2d856c5a1b7c10005c9c0fccaf3d491d4fbcc2a69bc54b5e95c5730c0874b run.py
1037dcb4f0831a3c96ca728527f939af1d3e19514b23ef54f663707875748ff8 run.sh
7026e676ee31916886f10feed959ffdbe486fda05b17421387e4717acbf90ba6 transcript.txt

Production Deployment Context

ContextForge's documentation describes registering MCP servers as gateways in a running ContextForge instance. If this sandbox server is reachable over HTTP in that pattern, any client that can reach the endpoint can submit the payload through tools/call.

Impact

An attacker with access to the python sandbox server HTTP endpoint can execute OS commands with the privileges of the server process. In containerized deployments with host mounts or internal network reachability, this can become filesystem compromise or network pivoting from the gateway host.

Suggested Fix

Remove raw getattr and setattr from safe builtins, expose only policy-controlled attribute access if dynamic lookup is required, replace substring filtering with a stricter RestrictedPython policy pipeline, and add authentication to HTTP transport for all tools/call requests.

Caveats

This report covers the python sandbox server sub-project. The core ContextForge gateway and proxy components are not directly affected. The Critical score assumes HTTP reachability; stdio-only deployments reduce the attack vector.

Correção

Protection Mechanism Failure

Code Injection

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Enumeração de Fraquezas

CWE-693CWE-94

Identificadores relacionados

CVE-2026-53710
GHSA-XM98-3VCF-FPH7
PYSEC-2026-3862

Produtos afetados

Mcp-Contextforge-Gateway