CVE-2026-0999 — Incorrect Implementation of Authentication Algorithm in Mattermost Mattermost-server

CWE-303 — Incorrect Implementation of Authentication Algorithm6 documents5 sources
Severity
4.3MEDIUMNVD
CNA5.4
EPSS
0.0%
top 85.41%
CISA KEV
Not in KEV
Exploit
No known exploits
Affected products
4
Github.com Mattermost Mattermost-serverGithub.com Mattermost Mattermost Server V8Mattermost Server+1 more
Timeline
PublishedFeb 16
Latest updateFeb 23

Description

Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to properly validate login method restrictions which allows an authenticated user to bypass SSO-only login requirements via userID-based authentication. Mattermost Advisory ID: MMSA-2025-00548

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:NExploitability: 2.8 | Impact: 1.4

Affected Packages4 packages

▶NVDmattermost/mattermost_server10.11.0 — 10.11.10+2
▶Gogithub.com/mattermost_mattermost-server< 5.3.2-0.20251212052346-61651b0df7ea+6
▶Gogithub.com/mattermost_mattermost_server_v8< 8.0.0-20251212052346-61651b0df7ea
▶CVEListV5mattermost/mattermost11.1.0 — 11.1.2+2

🔴Vulnerability Details

4
OSV
Mattermost fails to properly validate login method restrictions in github.com/mattermost/mattermost-server↗2026-02-23
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CVEList
Authentication bypass via userID login when email and username login are disabled↗2026-02-16
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GHSA
Mattermost fails to properly validate login method restrictions↗2026-02-16
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OSV
Mattermost fails to properly validate login method restrictions↗2026-02-16
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🕵️Threat Intelligence

1
Wiz
CVE-2026-0999 Impact, Exploitability, and Mitigation Steps | Wiz↗
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