CVE-2026-81092
MEDIUMDescription
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.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
Exploit Intelligence
Low risk: more likely to be exploited than 6% of all known CVEs.
References
Related Vulnerabilities
Other CWE-346 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-34291 | High | 8.8 | 84% | KEV | - |
| CVE-2009-1185 | High | 7.2 | 82% | - | Fix |
| CVE-2015-4495 | High | 8.8 | 71% | KEV | Fix |
| CVE-2020-16952 | High | 8.6 | 71% | - | - |
| CVE-2023-29711 | Critical | 9.8 | 70% | - | - |
| CVE-2024-23898 | High | 8.8 | 67% | - | Fix |
Common questions
How do I fix CVE-2026-81092?
No published fix for CVE-2026-81092 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-81092 being actively exploited?
Not that we know of. CVE-2026-81092 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.17% is the estimated probability that it will be exploited in the next 30 days. That is higher than 6% of all scored CVEs.
How severe is CVE-2026-81092?
CVE-2026-81092 has a CVSS v3 base score of 6.8, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-28.