What is CVE-2026-6340?

CVE-2026-6340 is a medium-severity vulnerability in Mattermost, classified under CWE-789. CVSS score: 4.3/10. Published 2026-05-18.

How severe is CVE-2026-6340?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Vulnerability in Mattermost

CVE-2026-6340

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate 7zip archive structure before processing which allows an authenticated attacker to cause server memory exhaustion and denial of service via upload…

EPSS: 0.000 (14.8th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L.

Affected products

Mattermost — versions 11.5.0, 10.11.0, 11.4.0
Mattermost Mattermost_server

Weakness classification (CWE)

CWE-789

References

responsibledisclosure@mattermost.com (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-6340?: CVE-2026-6340 is a medium-severity vulnerability in Mattermost, classified under CWE-789. CVSS score: 4.3/10. Published 2026-05-18.
How severe is CVE-2026-6340?: Medium severity. CVSS v3 base score is 4.3 out of 10.