id: GO-2026-4520
modules:
    - module: github.com/mattermost/mattermost-server
      vulnerable_at: 11.4.1+incompatible
    - module: github.com/mattermost/mattermost-server
      versions:
        - introduced: 10.11.0+incompatible
      vulnerable_at: 11.4.1+incompatible
    - module: github.com/mattermost/mattermost-server
      versions:
        - introduced: 11.1.0+incompatible
      vulnerable_at: 11.4.1+incompatible
    - module: github.com/mattermost/mattermost-server
      versions:
        - introduced: 11.2.0+incompatible
      vulnerable_at: 11.4.1+incompatible
    - module: github.com/mattermost/mattermost-server/v5
      non_go_versions:
        - fixed: 5.3.2-0.20251212052346-61651b0df7ea
      vulnerable_at: 5.39.3
    - module: github.com/mattermost/mattermost-server/v6
      vulnerable_at: 6.7.2
    - module: github.com/mattermost/mattermost/server/v8
      versions:
        - fixed: 8.0.0-20251212052346-61651b0df7ea
summary: Mattermost fails to properly validate login method restrictions in github.com/mattermost/mattermost-server
cves:
    - CVE-2026-0999
ghsas:
    - GHSA-3c9r-7f29-qp32
references:
    - advisory: https://github.com/advisories/GHSA-3c9r-7f29-qp32
    - advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-0999
    - web: https://github.com/mattermost/mattermost/commit/61651b0df7ea5db55d1e54f8d6fb5fce4149309c
    - web: https://mattermost.com/security-updates
notes:
    - fix: 'module merge error: could not merge versions of module github.com/mattermost/mattermost-server: introduced and fixed versions must alternate'
    - fix: 'github.com/mattermost/mattermost/server/v8: could not add vulnerable_at: could not find tagged version between introduced and fixed'
source:
    id: GHSA-3c9r-7f29-qp32
    created: 2026-02-23T12:11:46.52600457-05:00
review_status: UNREVIEWED