IBM has disclosed a regular expression denial of service (ReDoS) vulnerability in its ContextForge MCP Gateway that allows authenticated users to exhaust CPU resources and potentially disrupt service availability.
Quick Take
- What: CVE-2026-94407, a ReDoS vulnerability (CWE-1333) in IBM ContextForge MCP Gateway versions 1.0.0 through 1.0.11 with CVSS score 6.5
- Who is affected: Organizations running IBM ContextForge MCP Gateway versions 1.0.0 to 1.0.11
- Attack vector: Authenticated users with tool-registration privileges can embed catastrophically backtracking regex patterns in a tool’s JSON Schema pattern field
- Impact: Validation calls may consume unbounded CPU, potentially degrading gateway availability
- What to do: Upgrade to version 1.1.0 immediately
In plain English
IBM ContextForge MCP Gateway is a tool that validates data using patterns defined in JSON Schemas. A security flaw lets logged-in users who can register tools insert specially crafted regular expressions (text-matching patterns) that cause the system to work extremely hard when checking data. This can slow down or freeze the gateway, making it unavailable to other users.
What you should do: If you run this software, you need to upgrade to version 1.1.0. If you don’t use IBM ContextForge MCP Gateway, you can ignore this issue.
What happened
IBM ContextForge MCP Gateway validates tool arguments, tool results, and prompt arguments against JSON Schemas supplied by tool and prompt authors or by federated remote MCP servers. These schemas can contain regular expression keywords such as pattern and patternProperties.
The vulnerability exists because IBM ContextForge MCP Gateway evaluates regular expressions embedded in these schemas without any time or complexity bound. An authenticated user with tool-registration privileges can embed catastrophically backtracking regex patterns in a tool’s JSON Schema pattern field. When ContextForge validates arguments against that schema, the validation call may consume unbounded CPU, potentially degrading gateway availability.
IBM published the security bulletin on November 13, 2026. The vulnerability is tracked as CVE-2026-94407 and classified under CWE-1333 (Inefficient Regular Expression Complexity). IBM assigned a CVSS v3.1 base score of 6.5 with the vector (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H), indicating a network-exploitable vulnerability requiring low privileges with high availability impact.
What you should do
IBM strongly recommends upgrading to version 1.1.0 immediately. The company states there are no workarounds and emphasizes that organizations should address the vulnerability now.
Administrators running affected versions (1.0.0 through 1.0.11) should consult the v1.1.0 release notes and plan an immediate upgrade. IBM provides no mitigations short of upgrading to the fixed version.
What it means
This vulnerability highlights the risks of unbounded input validation in systems that process user-supplied schemas or patterns. While the attack requires authentication and specific privileges (tool-registration), it can be exploited remotely over the network with low complexity.
The ReDoS attack vector is particularly concerning for gateway infrastructure, where availability is critical. A single malicious or poorly crafted regular expression can monopolize CPU resources, creating a denial of service condition that affects all users of the gateway.
Organizations using IBM ContextForge MCP Gateway in production environments should treat this as a priority patch, especially if tool-registration privileges are granted to multiple users or if the gateway serves critical workloads.
