IBM ContextForge MCP Gateway SSRF via DNS Rebinding

Technical Analysis

The MCP Gateway acts as a broker between agents/clients and downstream MCP tool servers, and likely performs outbound HTTP requests based on client-supplied URLs or hostnames (e.g., for tool registration, resource fetching, or webhook callbacks). An attacker controls a DNS name that initially resolves to an allowed address to pass validation, then rebinds to an internal IP (e.g., cloud metadata service, internal admin panel) after the check, causing the gateway to issue requests on the attacker's behalf. Because the gateway sits at a trust boundary between external clients and internal agent/tool infrastructure, this SSRF crosses network segmentation, potentially leaking cloud credentials, internal service responses, or MCP server configuration data. The attack requires valid authentication to the gateway but no further privilege escalation, and the CVSS 8.2 score reflects high confidentiality impact with network-based, low-complexity exploitation.

Affected Systems

IBM ContextForge MCP Gateway; protocols: MCP

Detection Signatures

• Outbound requests from MCP gateway to unexpected internal IP ranges (RFC1918, 169.254.169.254) shortly after DNS resolution of an external-looking hostname
• Repeated/rapid DNS resolution changes for the same hostname (rebinding pattern) in gateway resolver logs
• Gateway logs showing URL/hostname parameters supplied in tool registration or resource-fetch requests that were not present in allow-lists
• Anomalous access to cloud metadata endpoints or internal admin services correlated with MCP gateway service account

Remediation Steps

1. 1

   Patch the gateway

   Apply IBM's fix for CVE-2026-77822 as soon as it is released; track the official advisory for patched versions.

2. 2

   Enforce strict URL/hostname allow-listing

   Validate and pin resolved IP addresses at request time (not just at initial validation) to prevent post-check DNS rebinding.

3. 3

   Network-layer egress controls

   Restrict the gateway's outbound network access to only required destinations using firewall rules or a proxy, blocking access to internal RFC1918 ranges and cloud metadata IPs.

4. 4

   Disable DNS rebinding via IP pinning

   Resolve hostnames once, cache the IP, and reuse the same IP for the connection lifetime rather than re-resolving mid-transaction.

5. 5

   Audit and monitor authentication

   Since exploitation requires authentication, review and tighten credential issuance for MCP gateway clients and monitor for anomalous authenticated request patterns.