CVE-2026-53710 in MCP Context Forge
Summary
by MITRE • 09/15/2026
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.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 09/15/2026
The vulnerability identified in MCP Context Forge prior to version 1.0.2 represents a critical failure in secure coding practices within its Python sandbox server component, specifically located in the python_sandbox_server module. As an AI gateway and proxy supporting multiple API standards including MCP, A2A, REST, and gRPC, this software handles sensitive code execution requests that are central to its function as an intermediary for artificial intelligence workloads. The core technical flaw stems from a flawed implementation of runtime code validation within the server_fastmcp.py file. Instead of employing robust isolation mechanisms or strict allow-listing of permissible attributes, the system exposes raw getattr functionality through safe_builtins while omitting essential guards such as getattr. This architectural weakness allows an attacker to bypass intended restrictions by dynamically constructing dunder names at runtime, effectively traversing the Python class hierarchy in ways that were not anticipated by the developers.
From a technical perspective, this flaw enables arbitrary code execution with the privileges of the server process. By leveraging the execute_code MCP tool, which is designed for safe script evaluation within an isolated environment, an attacker can manipulate attribute access to reach dangerous standard library modules like subprocess.Popen. Once access to Popen is achieved, the attacker gains full control over operating system command execution. This capability transforms a sandboxed code interpreter into a remote shell equivalent, allowing for complete compromise of the underlying host infrastructure. The vulnerability aligns closely with CWE-94 Improper Control of Generation of Code or Command and CWE-78 OS Command Injection, as it involves the injection of malicious commands through improper validation of user-supplied input that ultimately reaches system-level execution functions.
The operational impact of this vulnerability is severe due to its potential for remote exploitation depending on the deployment configuration. When MCP Context Forge operates using HTTP or Server-Sent Events transports, the execute_code tool may be exposed without requiring authentication, creating a direct attack vector over the network. This means that any entity capable of reaching the service endpoint can potentially exploit this flaw to gain unauthorized access to the server environment. In contrast, deployments utilizing only stdio transport have reduced network reachability, which limits exposure but does not eliminate risk if local users or compromised processes interact with the tool. The attack path is well-documented in MITRE ATT&CK frameworks under techniques such as T1059 Command and Scripting Interpreter and potentially T1203 Exploitation for Client Execution, highlighting how attackers leverage legitimate software features to achieve persistence or privilege escalation within enterprise environments.
Mitigation strategies must prioritize immediate version upgrades alongside architectural reviews of sandbox implementations. The most effective remediation is upgrading MCP Context Forge to version 1.0.2 or later, where the developers have addressed these specific flaws by implementing stricter validation logic and removing unsafe attribute access patterns. For organizations unable to upgrade immediately due to dependency constraints, network-level controls such as firewalls should be configured to restrict access to the execute_code endpoint exclusively from trusted sources if authentication is not enabled. Additionally, running the python_sandbox_server with minimal privileges using principles of least privilege can limit the damage caused by successful exploitation. Future development cycles must enforce rigorous static analysis and dynamic testing focused on code injection vectors, ensuring that sandbox environments do not expose internal object hierarchies or built-in functions that could be leveraged for escape attacks.