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Vulnerabilities

Vulnerability · CVE-2026-0999

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

Published Feb 16, 2026 · catalog updated Feb 17, 2026 · Mattermost Mattermost

Last checked Nov 12, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-0999. EPSS is 0.20%. Act only if a listed version of Mattermost Mattermost is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
Medium5.4
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.20%
Remediation
Advisory link
Affected products
vendor Mattermost Mattermost 11.2.0 ≤11.2.1

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

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor Mattermost Mattermost 11.2.0 ≤11.2.111.2.0 ≤11.2.1

How to fix CVE-2026-0999

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-0999. EPSS is 0.20%. Act only if a listed version of Mattermost Mattermost is installed.

Which versions are affected?

Compare what you have installed with Mattermost Mattermost 11.2.0 ≤11.2.1 11.2.0 ≤11.2.1. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.20%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Feb 16, 2026 · EUVD

    Detected

    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

  2. Feb 17, 2026 · EUVD

    Updated

    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

Sources

  • CVE.orgVulnerability recordCVE-2026-0999

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-0999

    30-day exploitation probability 0.20%

    first.org
  • EUVDVulnerability recordEUVD-2026-6102

    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

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Nov 12, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSNov 12, 2026
  • CVE.orgNov 10, 2026
  • EUVDNov 9, 2026