What is CVE-2026-9693?

CVE-2026-9693 is a low-severity vulnerability in Mattermost, classified under Incomplete Cleanup. CVSS score: 3.5/10. Published 2026-08-17.

How severe is CVE-2026-9693?

Low severity. CVSS v3 base score is 3.5 out of 10.

Vulnerability in Mattermost

CVE-2026-9693

Mattermost versions 10.11.x <= 10.11.20, 11.7.x <= 11.7.5 Mattermost fails to remove thread membership records when a user is removed from or leaves a team, which allows a previously removed user who is later re-invited to the team to view private channel thread root post content and metadata via the team threads API.. Mattermost Advisory ID: MMSA-2026-00682

Published 2026-08-17 · last modified 2026-08-19.

CVSS v3 metric

CVSS v3 base score 3.5 (Low). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.003 (17.5th percentile), scored 2026-10-02.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 17th percentile — 17.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001

Affected products

Mattermost — versions 10.11.0, 11.7.0, 11.9.0
Mattermost Server

Weakness classification (CWE)

CWE-459 — Incomplete Cleanup

References

mattermost.com/security-updates (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-9693?: CVE-2026-9693 is a low-severity vulnerability in Mattermost, classified under Incomplete Cleanup. CVSS score: 3.5/10. Published 2026-08-17.
How severe is CVE-2026-9693?: Low severity. CVSS v3 base score is 3.5 out of 10.