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CVE-2026-2455

4.3 mediumEPSS 0.2%

Medium (4.3) in mattermost mattermost server. EPSS 0.2% chance of exploitation in the next 30 days. Fixed in github.com/mattermost/mattermost/server/v8 8.0.0-20260129133647-5d787969c2d5.

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

Severity

CVSS 3.1

4.3 medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
EPSS
0.2% chance of exploitation in the next 30 days; higher than 6% of CVEs (scores of 2026-10-31)
CWE
CWE-918
Published
Modified
Record from
the NVD, synced

Affected

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-gqv7-j2j8-qmwqGogithub.com/mattermost/mattermost/server/v8<8.0.0-20260129133647-5d787969c2d58.0.0-20260129133647-5d787969c2d5
GHSA-gqv7-j2j8-qmwqGogithub.com/mattermost/mattermost-server<5.3.2-0.20260129133647-5d787969c2d55.3.2-0.20260129133647-5d787969c2d5
GHSA-gqv7-j2j8-qmwqGogithub.com/mattermost/mattermost-server>=10.11.0-rc1 <10.11.1110.11.11
GHSA-gqv7-j2j8-qmwqGogithub.com/mattermost/mattermost-server>=11.2.0-rc1 <11.2.311.2.3
GHSA-gqv7-j2j8-qmwqGogithub.com/mattermost/mattermost-server>=11.3.0-rc1 <11.3.111.3.1
GO-2026-4746Gogithub.com/mattermost/mattermost-server>=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		10.11.11+incompatible, 11.2.3+incompatible, 11.3.1+incompatible
GO-2026-4746Gogithub.com/mattermost/mattermost-server/v5all versionsno fix published
GO-2026-4746Gogithub.com/mattermost/mattermost-server/v6all versionsno fix published
GO-2026-4746Gogithub.com/mattermost/mattermost/server/v8<8.0.0-20260129133647-5d787969c2d58.0.0-20260129133647-5d787969c2d5

References

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