cve.bz

CVE-2026-4274

5.4 mediumEPSS 0.1%

Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel via sending crafted membership sync messages that trigger team membership assignment. Mattermost Advisory ID: MMSA-2026-00574

Severity

CVSS 3.1

5.4 medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
EPSS
0.1% chance of exploitation in the next 30 days; higher than 3% of CVEs (scores of 2026-10-31)
CWE
CWE-863
Published
Modified
Record from
the NVD, synced

Affected

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-g7fp-cqj5-x8hfGogithub.com/mattermost/mattermost/server/v8>=11.4.0-rc1 <11.4.111.4.1
GHSA-g7fp-cqj5-x8hfGogithub.com/mattermost/mattermost/server/v8>=11.3.0-rc1 <11.3.211.3.2
GHSA-g7fp-cqj5-x8hfGogithub.com/mattermost/mattermost/server/v8>=11.2.0-rc1 <11.2.311.2.3
GHSA-g7fp-cqj5-x8hfGogithub.com/mattermost/mattermost/server/v8>=10.11.0-rc1 <10.11.1110.11.11
GHSA-g7fp-cqj5-x8hfGogithub.com/mattermost/mattermost/server/v8>=8.0.0-20260105080200-d27a2195068d <8.0.0-20260217110922-b7d4a1f1f59b8.0.0-20260217110922-b7d4a1f1f59b
GO-2026-5393Gogithub.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 <11.3.2+incompatible
>=11.4.0-rc1+incompatible <11.4.1+incompatible		10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatible
GO-2026-5393Gogithub.com/mattermost/mattermost-server/v5all versionsno fix published
GO-2026-5393Gogithub.com/mattermost/mattermost-server/v6all versionsno fix published
GO-2026-5393Gogithub.com/mattermost/mattermost/server/v8>=8.0.0-20260105080200-d27a2195068d <8.0.0-20260217110922-b7d4a1f1f59b8.0.0-20260217110922-b7d4a1f1f59b

References

Check your stackJSON