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CVE-2026-25783

4.3 mediumEPSS 0.3%

Medium (4.3) in mattermost mattermost server. EPSS 0.3% chance of exploitation in the next 30 days. Fixed in github.com/mattermost/mattermost/server/v8 8.0.0-20260129181235-1346cf529aef.

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate User-Agent header tokens which allows an authenticated attacker to cause a request panic via a specially crafted User-Agent header. Mattermost Advisory ID: MMSA-2026-00586

Severity

CVSS 3.1

4.3 medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
EPSS
0.3% chance of exploitation in the next 30 days; higher than 22% of CVEs (scores of 2026-10-31)
CWE
CWE-1287
Published
Modified
Record from
the NVD, synced

Affected

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-2v3w-6g35-5f9vGogithub.com/mattermost/mattermost/server/v8<8.0.0-20260129181235-1346cf529aef8.0.0-20260129181235-1346cf529aef
GHSA-2v3w-6g35-5f9vGogithub.com/mattermost/mattermost-server<5.3.2-0.20260129181235-1346cf529aef5.3.2-0.20260129181235-1346cf529aef
GHSA-2v3w-6g35-5f9vGogithub.com/mattermost/mattermost-server>=10.11.0-rc1 <10.11.1110.11.11
GHSA-2v3w-6g35-5f9vGogithub.com/mattermost/mattermost-server>=11.2.0-rc1 <11.2.311.2.3
GHSA-2v3w-6g35-5f9vGogithub.com/mattermost/mattermost-server>=11.3.0-rc1 <11.3.111.3.1
GO-2026-4725Gogithub.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-2026-4725Gogithub.com/mattermost/mattermost-server/v5all versionsno fix published
GO-2026-4725Gogithub.com/mattermost/mattermost-server/v6all versionsno fix published
GO-2026-4725Gogithub.com/mattermost/mattermost/server/v8<8.0.0-20260129181235-1346cf529aef8.0.0-20260129181235-1346cf529aef

References

Check your stackJSON