CVE-2026-2455

Description

Mattermost fails to canonicalize IPv4-mapped IPv6 addresses before reserved IP validation 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 v5.3.2-0.20260129133647-5d787969c2d5.

How to fix CVE-2026-2455

To remediate CVE-2026-2455, upgrade the affected package to a fixed version below.

• —upgrade to 5.3.2-0.20260129133647-5d787969c2d5 or later
• —upgrade to 10.11.11+incompatible or later
• —no fix listed
• —no fix listed
• —upgrade to 8.0.0-20260129133647-5d787969c2d5 or later
• —upgrade to 8.0.0-20260129133647-5d787969c2d5 or later

Is CVE-2026-2455 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.

Affected packages (6)

• from 0, < 5.3.2-0.20260129133647-5d787969c2d5
• >= 10.11.0-rc1+incompatible, < 10.11.11+incompatible, >= 11.2.0-rc1+incompatible, < 11.2.3+incompatible, >= 11.3.0-rc1+incompatible, < 11.3.1+incompatible
• from 0
• from 0
• from 0, < 8.0.0-20260129133647-5d787969c2d5
• from 0, < 8.0.0-20260129133647-5d787969c2d5

CVSS scores

References (5)

• ADVISORYgithub.com/advisories/GHSA-gqv7-j2j8-qmwq
• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-2455
• PATCHgithub.com/mattermost/mattermost
• WEBgithub.com/mattermost/mattermost/commit/5d787969c2d5ab591a9dcd61b0810475eed7a646
• WEB