CVE-2026-2455: Mattermost fails to canonicalize IPv4-mapped IPv6 addresses before reserved IP validation

March 16, 2026 (updated March 18, 2026)

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to canonicalize IPv4-mapped IPv6 addresses before reserved IP validation which allows an attacker to perform SSRF attacks against internal services via IPv4-mapped IPv6 literals (e.g., [::ffff:127.0.0.1]).. Mattermost Advisory ID: MMSA-2026-00585

References

github.com/advisories/GHSA-gqv7-j2j8-qmwq
github.com/mattermost/mattermost
github.com/mattermost/mattermost/commit/5d787969c2d5ab591a9dcd61b0810475eed7a646
mattermost.com/security-updates
nvd.nist.gov/vuln/detail/CVE-2026-2455

Code Behaviors & Features

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