data/reports/GO-2026-5360.yaml

id: GO-2026-5360
modules:
    - module: github.com/mattermost/mattermost-server
      versions:
        - introduced: 10.11.0-rc1+incompatible
        - fixed: 10.11.12+incompatible
        - introduced: 11.2.0-rc1+incompatible
        - fixed: 11.2.4+incompatible
        - introduced: 11.3.0-rc1+incompatible
        - fixed: 11.3.2+incompatible
        - introduced: 11.4.0-rc1+incompatible
        - fixed: 11.4.1+incompatible
      vulnerable_at: 11.4.1-rc2+incompatible
    - module: github.com/mattermost/mattermost-server/v5
      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:
        - introduced: 8.0.0-20260105080200-d27a2195068d
        - fixed: 8.0.0-20260217110922-b7d4a1f1f59b
summary: |-
    Mattermost allows attackers to take over arbitrary user accounts via overly
    permissive substring matching flaw in github.com/mattermost/mattermost-server
cves:
    - CVE-2026-27656
ghsas:
    - GHSA-fg35-5rf6-qg3g
references:
    - advisory: https://github.com/advisories/GHSA-fg35-5rf6-qg3g
    - advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-27656
    - web: https://mattermost.com/security-updates
notes:
    - fix: 'github.com/mattermost/mattermost/server/v8: could not add vulnerable_at: could not find tagged version between introduced and fixed'
source:
    id: GHSA-fg35-5rf6-qg3g
    created: 2026-06-25T02:53:57.67086574-04:00
review_status: UNREVIEWED