CVE-2026-108859: mark3labs mcp-go

mcp-go through 1.2.1 Denial of Service via Unbounded POST Body Buffering

CVSS 8.7 HighEPSS 0.0054 · 45th percentile

Published by the CVE Program (CNA: VulnCheck) at 11 Oct 2026, 13:26 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it.

Affected products, as the CNA wrote them
Vendor	Product	Versions
mark3labs	mcp-go pkg:golang/github.com/mark3labs/mcp-go	affected 1.2.1 and earlier semver Other versions: unaffected

Identifiers

CVE-2026-108859

CNA

VulnCheck

Weakness (CWE)

CWE-770

Not analysed yet

We haven’t published our own analysis of this CVE. If a person reviews it, this page will say what’s affected and what has to be true for it to matter.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
8.7	High	4.0	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N	CNA (VulnCheck)Used for this record
7.5	High	3.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	CNA (VulnCheck)

CISA KEV Not listed.
EPSS 0.0054, the 45th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

This record came from the full history of the CVE Program, published 11 Oct 2026. New records show when each source confirmed them.

Sources

References from the CNA

hackmd.io/@1ExmmukzRMWN7B4gQ4W-4Q/mark3labs-mcp-go-streamable-http-unbounded-body third-party-advisory
github.com/mark3labs/mcp-go/blob/90d247ed8d45cbb7d71d9a95e112789b78760443/server/streamable_http.go#L405-L411 technical-description
github.com/mark3labs/mcp-go product
www.vulncheck.com/advisories/mcp-go-through-1.2.1-denial-of-service-via-unbounded-post-body-buffering third-party-advisory

Facts on this page come from the CVE List as the CNA published them, with CVSS from the sources named above, CISA KEV and FIRST EPSS. Vendors, products and versions are shown as the CNA wrote them. We don’t reproduce the CVE’s description.