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TI-2026-56054 Aliases CVE-2026-81092GHSA-8g5x-gj7x-mxgm

mcp-go before 0.56.0 Missing Host Header Validation Enables DNS Rebinding

Priority LOW 33CWE-346Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Passive
Attack complexity
Low
Attack requirements
Present
Impact type
Security bypass
Confidentiality · integrity · availability
High · High · None
Fix status
Partial Red Hat: 1 fixed, 3 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-346.

Summary

mcp-go accepted requests on its HTTP transports without checking the Host header. StreamableHTTPServer.ServeHTTP in server/streamable_http.go and SSEServer.ServeHTTP in server/sse.go served any request arriving over a loopback connection regardless of the host it named, and the SSE transport's cross-origin default allowed any origin. A page in a browser could therefore point a name it controlled at the loopback address and reach a server listening there, invoking tools and reading resources that the server exposed on the assumption that only local software could connect. No release before 0.56.0 validated the header on either transport; 0.56.0 adds server/http_localhost.go, which rejects a loopback-bound request carrying a host that is not a loopback name, and wires it into both transports.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00223 13th percentileScored 2026-11-07
Fix Partial mcp-go (mark3labs): 0.56.0Red Hat: 3 advisoriesRed Hat: 1 fixed, 3 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
mark3labsmcp-gobefore 0.56.00.56.0Patch availableCNA
  • mcp-go Vendormark3labs Affected before 0.56.0 Fixed in 0.56.0 Patch available CNA

Remediation

  • Fix · CNA mcp-go (mark3labs) Fixed in 0.56.0

Red Hat 3 advisories

  • RHSA-2026:62537 Released 2026-09-02 · Red Hat rating Moderate
    Red Hat Hardened Images RPMs Security Update
    • Red Hat Hardened Images tempo3.0-3.0.3-0.2.hum1@aarch64, tempo3.0-3.0.3-0.2.hum1@src, tempo3.0-3.0.3-0.2.hum1@x86_64
  • RHSA-2026:62527 Released 2026-09-02 · Red Hat rating Moderate
    Red Hat Hardened Images RPMs Security Update
    • Red Hat Hardened Images tempo2.10-2.10.8-0.2.hum1@aarch64, tempo2.10-2.10.8-0.2.hum1@src, tempo2.10-2.10.8-0.2.hum1@x86_64
  • RHSA-2026:54874 Released 2026-08-14 · Red Hat rating Moderate
    Red Hat Hardened Images RPMs bug fix and enhancement update
    • Red Hat Hardened Images tempo3-0-main@aarch64, tempo3-0-main@src, tempo3-0-main@x86_64

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Connectivity Link 1AffectedNo fix yet: Fix deferred
Red Hat OpenShift AI (RHOAI)AffectedNo fix yet: Fix deferred
Red Hat OpenShift distributed tracing 3AffectedNo fix yet: Fix deferred
Red Hat Hardened ImagesFixed RHSA-2026:54874, RHSA-2026:62527

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-81092
  2. 2026-10-03 Alias added: GHSA-8g5x-gj7x-mxgm

References

Patch 1

Other 2

  • TI-2026-70749 mcp-go Denial of Service via Unbounded POST Body Buffering CVSS 4.0HIGH 8.7
  • TI-2026-85606 Origin validation error in mcp-go lets malicious servers obtain tokens CVSS 4.0MEDIUM 5.1

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences