7.6

CVE-2026-81092: mcp-go before 0.56.0 Missing Host Header Validation Enables DNS Rebinding

Deferred
AliasesRHSA-2026:54874
Published 27-08-2026Last modified 29-08-2026

Vulnerability summary

CVE-2026-81092 is a high (CVSS 7.6) Origin Validation Error vulnerability in mark3labs mcp-go. EPSS estimates a 0.22% chance of exploitation in the next 30 days, higher than 13% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 7.6, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
7.6/10
010
High · v4.0 (CVE.org)
EPSS score
0.22%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 6 · Related 4
OPENSUSE-SU-2026:11670-1OPENSUSE-SU-2026:21771-1RHSA-2026:62527RHSA-2026:62537SUSE-SU-2026:23496-1SUSE-SU-2026:23636-1

Timeline

  1. 27-08-2026
    PublishedVulnerability first disclosed.
  2. 29-08-2026
    Last modifiedVulnerability 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

5 scores · 3 sources · 2 versions

EPSS trend

Probability

0.22%

Chance of exploitation in the next 30 days

Percentile

13%

Versus all other CVEs

30-day change

No change 0.00 pp

From 0.22% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, user interaction (CVSS vector). Other conditions: not stated in public data.

Mark3labs1 product
Redhat1 product
  • tempo3.0< 0:3.0.3-0.1.hum1

2 vendors · 2 products

References

12 links
Show all 12 references