Vulnerability · Published Feb 16, 2026 · Assigned by Mattermost
CVE-2026-0999Authentication bypass via userID login when email and username login are disabled
Medium 5.4
In plain English
A medium-severity security flaw in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 10% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)5.4Medium
Exploit odds (30 days)0.2%top 90.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official 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
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | no fix listed | GO-2026-4520 |
| Go | github.com/mattermost/mattermost-server | no fix listed | GHSA-3c9r-7f29-qp32 |
| Go | github.com/mattermost/mattermost-server | no fix listed | GHSA-3c9r-7f29-qp32 |
| Go | github.com/mattermost/mattermost-server | no fix listed | GHSA-3c9r-7f29-qp32 |
| Go | github.com/mattermost/mattermost-server | 5.3.2-0.20251212052346-61651b0df7ea | GHSA-3c9r-7f29-qp32 |
| Go | github.com/mattermost/mattermost-server | no fix listed | GO-2026-4520 |
| Go | github.com/mattermost/mattermost-server | no fix listed | GO-2026-4520 |
| Go | github.com/mattermost/mattermost-server | no fix listed | GO-2026-4520 |
| Go | github.com/mattermost/mattermost-server/v5 | no fix listed | GO-2026-4520 |
| Go | github.com/mattermost/mattermost-server/v6 | no fix listed | GO-2026-4520 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20251212052346-61651b0df7ea | GO-2026-4520 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20251212052346-61651b0df7ea | GHSA-3c9r-7f29-qp32 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 11.1.0 – through 11.1.210.11.0 – through 10.11.911.2.0 – through 11.2.1 |
Weakness: CWE-303 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
References
- MMSA-2025-00548 vendor-advisory