PT-2026-8324 · Mattermost · Mattermost

Daw10 · CVE-2026-0999 · Published 2026-02-16 · Updated 2026-03-03

Positive Technologies (AI Summary)

CVSS v3.1

5.4

Medium

Base vector

AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

Name of the Vulnerable Software and Affected Versions Mattermost versions 10.11.x through 10.11.9 Mattermost versions 11.1.x through 11.1.2 Mattermost versions 11.2.x through 11.2.1

Description The software does not properly validate login method restrictions. This allows an authenticated user to bypass Single Sign-On (SSO)-only login requirements by using userID-based authentication. The Mattermost Advisory ID for this issue is MMSA-2025-00548.

Recommendations Update Mattermost to a version later than 10.11.9. Update Mattermost to a version later than 11.1.2. Update Mattermost to a version later than 11.2.1.

Exploit

Fix

DoS

Weakness Enumeration

CWE-303

Related Identifiers

CVE-2026-0999

GHSA-3C9R-7F29-QP32

GO-2026-4520

SUSE-SU-2026:0757-1

Affected Products

Mattermost

References · 119

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/0xxx/CVE-2026-0999.json · Exploit
• https://mattermost.com/security-updates · Vendor Advisory
• https://osv.dev/vulnerability/GO-2026-4520 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-0999 · Security Note
• https://osv.dev/vulnerability/SUSE-SU-2026:0757-1 · Vendor Advisory
• https://osv.dev/vulnerability/GHSA-3c9r-7f29-qp32 · Vendor Advisory
• https://osv.dev/vulnerability/CVE-2026-0999 · Vendor Advisory
• https://github.com/mattermost/mattermost · Note
• https://github.com/mattermost/mattermost/commit/61651b0df7ea5db55d1e54f8d6fb5fce4149309c · Note
• https://suse.com/security/cve/CVE-2017-18903 · Note
• https://suse.com/security/cve/CVE-2026-27111 · Note
• https://suse.com/security/cve/CVE-2017-18918 · Note
• https://suse.com/security/cve/CVE-2026-27017 · Note
• https://github.com/advisories/GHSA-3c9r-7f29-qp32 · Note
• https://suse.com/security/cve/CVE-2026-25591 · Note