CVE-2026-0999

Description

Mattermost fails to properly validate login method restrictions in github.com/mattermost/mattermost-server. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: github.com/mattermost/mattermost-server/v5 before v5.3.2-0.20251212052346-61651b0df7ea.

How to fix CVE-2026-0999

To remediate CVE-2026-0999, upgrade the affected package to a fixed version below.

• —no fix listed
• —no fix listed
• —no fix listed
• —no fix listed
• —upgrade to 8.0.0-20251212052346-61651b0df7ea or later
• —upgrade to 8.0.0-20251212052346-61651b0df7ea or later

Is CVE-2026-0999 being exploited?

Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.

Affected packages (6)

• >= 11.1.0
• from 0
• from 0
• from 0
• from 0, < 8.0.0-20251212052346-61651b0df7ea
• from 0, < 8.0.0-20251212052346-61651b0df7ea

CVSS scores

References (5)

• ADVISORYgithub.com/advisories/GHSA-3c9r-7f29-qp32
• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-0999
• PATCHgithub.com/mattermost/mattermost
• WEBgithub.com/mattermost/mattermost/commit/61651b0df7ea5db55d1e54f8d6fb5fce4149309c
• WEB