MCP Context Forge is an AI gateway, registry, and proxy for MCP, A2A, REST, and gRPC APIs. Prior to 1.0.2, the python_sandbox_server in mcp-servers/python/python_sandbox_server/src/python_sandbox_server/server_fastmcp.py exposes raw getattr through safe_builtins, omits a required _getattr_ guard, and relies on validate_code checks for literal dangerous dunder strings. An attacker can construct dunder names at runtime, traverse the Python class hierarchy, reach subprocess.Popen, and execute OS commands with the server process privileges through the execute_code MCP tool. The HTTP/SSE transport can expose this tool without authentication, while stdio-only deployments have reduced network reachability. The issue affects the python_sandbox_server subproject and does not directly affect the core Context Forge gateway or proxy components. This issue is fixed in version 1.0.2.

Affected: PyPI: mcp-contextforge-gateway

**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:

```text beb2d856c5a1b7c10005c9c0fccaf3d491d4fbcc2a69bc54b5e95c5730c0874b run.py 1037dcb4f0831a3c96ca728527f939af1d3e19514b23ef54f663707875748ff8 run.sh 7026e676ee31916886f10feed959ffdbe486fda05b17421387e4717acbf90ba6 transcript.txt ```

## Production Deployment Context

ContextForge's documentation de…

Affected: PyPI: mcp-contextforge-gateway

**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:

```text beb2d856c5a1b7c10005c9c0fccaf3d491d4fbcc2a69bc54b5e95c5730c0874b run.py 1037dcb4f0831a3c96ca728527f939af1d3e19514b23ef54f663707875748ff8 run.sh 7026e676ee31916886f10feed959ffdbe486fda05b17421387e4717acbf90ba6 transcript.txt ```

## Production Deployment Context

ContextForge's documentation de…