CVE-2026-81092

Aliases:RHSA-2026:54874RHSA-2026:62527RHSA-2026:62537
Advisory lineage Upstream: 0 Downstream: 3
Received
Published: 27 Aug 2026, 14:50
Last modified:29 Aug 2026, 11:48

Vulnerability Summary

Overall Risk (default)
medium
30/100
CVSS Score
7.6 HIGH
v4.0 (cve.org)
EPSS Score
0.17% LOW
0% probability 0.00%
KEV
Not listed
Ransomware
No reports
Public exploits
None found
Dark Web
Not detected

Timeline

27 Aug 2026, 14:50
Published
Vulnerability first disclosed
29 Aug 2026, 11:48
Last Modified
Vulnerability information updated

Description

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.

CVSS Metrics

  • v4.0•HIGH•Score: 7.6CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
  • v4.0•HIGH•Score: 7.6CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
  • v3.1•MEDIUM•Score: 6.8CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N

EPSS Trends

Current EPSS score: 0.17%• Percentile: 6%

Techniques & Countermeasures

  • CWE-346•Origin Validation Error

    The product does not properly verify that the source of data or communication is valid.

Affected Systems

  • mark3labs•mcp-go

    < 0.56.0

  • redhat•tempo2.10

    < 0:2.10.8-0.2.hum1

  • redhat•tempo3.0

    < 0:3.0.3-0.1.hum1 | < 0:3.0.3-0.2.hum1

References (16)