vulnerability / NVI-00011801 / Revision 3
mcp-contextforge-gateway has RestrictedPython sandbox bypass via getattr builtin in python_sandbox_server
GitHub lists this reviewed advisory for mcp-contextforge-gateway. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
10 critical
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
10 CRITICAL (3.1)
security-advisories@github.com severity; no combined Null risk score.
1.141%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.66675. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
mcp-contextforge-gateway
source listed<= 1.0.1
**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\nb'IBM_SANDBOX_POC_PASS'\n" IBM_RESTRICTEDPYTHON_GETATTR_POPEN_REPRO_PASS ``` PoC artifact hashes: ```tex
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-xm98-3vcf-fph7 ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-53710 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-53710 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 3 ·
Source facts changed; compare the preserved prior revision.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.