Red Hat Security Advisory: Red Hat Hardened Images RPMs Security Update

CVE-2026-81092 is a vulnerability in the mcp-go component used by Red Hat Hardened Images RPMs (tempo3.0) where the Host header in HTTP requests is not properly validated in the StreamableHTTPServer and SSEServer transports. This allows a remote attacker to perform a DNS rebinding attack by directing a controlled domain name to the loopback address, bypassing local network restrictions and potentially accessing local services. The vulnerability is classified under CWE-918 (Server-Side Request Forgery). Red Hat notes that exploitation requires a browser running JavaScript on the same host as the mcp-go HTTP server, a condition not met in typical Red Hat Kubernetes/OpenShift deployments. Red Hat has released a fixed version of the affected RPMs incorporating mcp-go v0.56.0, which includes the necessary Host header validation. Until the update is applied, mitigations such as network restrictions and reverse proxy Host header validation are recommended.

If exploited, this vulnerability could allow an attacker to bypass local network restrictions via DNS rebinding, potentially leading to unauthorized access to local services and information disclosure. The CVSS base score assigned by Red Hat is 6.8 (medium severity) reflecting high confidentiality and integrity impact but requiring user interaction and high attack complexity. However, Red Hat's typical deployment environments do not meet the conditions for exploitation, reducing practical risk in those contexts.

A fixed update is available in tempo3.0-3.0.3-0.2.hum1 RPMs which include mcp-go v0.56.0 with proper Host header validation. Users should apply this update promptly. Where immediate update is not possible, restrict inbound connections to trusted clients using network policies or firewall rules, and deploy a reverse proxy in front of the MCP endpoint to enforce strict Host header validation. Red Hat does not indicate any 'no action required' status; thus, applying the update or mitigations is recommended.