What is CVE-2026-10103?

CVE-2026-10103 is a medium-severity vulnerability in Mattermost, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 4.3/10. Published 2026-07-13.

How severe is CVE-2026-10103?

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

Auth bypass in Mattermost

CVE-2026-10103

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to verify post ownership in the shared channel inbound sync handler, which allows an authenticated remote cluster to modify or delete posts authored by local users or other remotes via crafted sync messages referencing arbitrary post IDs in channels shared with that remote.. Mattermost Advisory ID: MMSA-2026-00689

Vulnerability class: IDOR (Insecure Direct Object Reference)

Published 2026-07-13 · last modified 2026-07-14.

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:L/A:N.

EPSS exploit prediction

EPSS: 0.002 (14.1th percentile), scored 2026-10-12.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 14th percentile — 14.1% 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: 0.002 · change: 0.000

Affected products

Mattermost — versions 11.7.0, 11.6.0, 10.11.0
Mattermost Server

Weakness classification (CWE)

CWE-639 — Authorization Bypass Through User-Controlled Key

References

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

Frequently asked questions

What is CVE-2026-10103?: CVE-2026-10103 is a medium-severity vulnerability in Mattermost, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 4.3/10. Published 2026-07-13.
How severe is CVE-2026-10103?: Medium severity. CVSS v3 base score is 4.3 out of 10.