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CVE-2026-6046

5.3 mediumEPSS 0.2%

Medium (5.3) in mattermost mattermost server. EPSS 0.2% chance of exploitation in the next 30 days. Fixed in github.com/mattermost/mattermost-server 10.11.17, 10.11.17+incompatible, 11.5.5.

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649

Severity

CVSS 3.1

5.3 medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
EPSS
0.2% chance of exploitation in the next 30 days; higher than 8% of CVEs (scores of 2026-10-31)
CWE
CWE-200
Published
Modified
Record from
the NVD, synced

Affected

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-3vmp-whvv-5v9vGogithub.com/mattermost/mattermost-server>=11.6.0 <11.6.111.6.1
GHSA-3vmp-whvv-5v9vGogithub.com/mattermost/mattermost-server>=11.5.0 <11.5.511.5.5
GHSA-3vmp-whvv-5v9vGogithub.com/mattermost/mattermost-server>=10.11.0 <10.11.1710.11.17
GHSA-3vmp-whvv-5v9vGogithub.com/mattermost/mattermost/server/v8>=8.0.0-20250731163400-5b955468ea1e <8.0.0-20260428151657-c79c3831061a8.0.0-20260428151657-c79c3831061a
GO-2026-6279Gogithub.com/mattermost/mattermost-server>=10.11.0+incompatible <10.11.17+incompatible
>=11.5.0+incompatible <11.5.5+incompatible
>=11.6.0+incompatible <11.6.1+incompatible		10.11.17+incompatible, 11.5.5+incompatible, 11.6.1+incompatible
GO-2026-6279Gogithub.com/mattermost/mattermost-server/v5all versionsno fix published
GO-2026-6279Gogithub.com/mattermost/mattermost-server/v6all versionsno fix published
GO-2026-6279Gogithub.com/mattermost/mattermost/server/v8>=8.0.0-20250731163400-5b955468ea1e <8.0.0-20260428151657-c79c3831061a8.0.0-20260428151657-c79c3831061a

References

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