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CVE record · CVE-2026-4339

SSRF via unvalidated attachment URLs in Mattermost Agents plugin MCP server

CVSS 6.5 MediumEPSS 0.0014 · 3rd percentile

Published by the CVE Program (CNA: Mattermost) at 26 Jun 2026, 14:44 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
VendorProductVersions
Mattermost Mattermost
  • affected 10.11.0 to 10.11.18, inclusive semver
  • affected 11.6.0 to 11.6.3, inclusive semver
  • affected 11.5.0 to 11.5.6, inclusive semver
  • unaffected 11.7.0
  • unaffected 10.11.19
  • unaffected 11.6.4
  • unaffected 11.5.7
Other versions: unaffected
Identifiers
CVE-2026-4339
CNA
Mattermost
Weakness (CWE)
CWE-918
Tags
Published
26 Jun 2026
Updated
26 Jun 2026

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

ScoreRatingCVSSVectorSource
6.5 Medium 3.1 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N CNA (Mattermost)
  • CISA KEV Not listed.
  • EPSS 0.0014, the 3rd percentile, on 5 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 26 Jun 2026. New records show when each source confirmed them.

Sources

References from the CNA

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.