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CVE-2026-25783 Moderate

Mattermost fails to properly validate User-Agent header tokens in github.com/mattermost/mattermost-server

Mattermost fails to properly validate User-Agent header tokens in github.com/mattermost/mattermost-server. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: github.com/mattermost/mattermost-server/v5 before v5.3.2-0.20260129181235-1346cf529aef.

Exploit probability 0.3%
Published March 26, 2026
Required by Not available
Last source change March 26, 2026

02 / AFFECTED SOFTWARE

Affected packages

Unknown Unknown

34 explicit affected versions

Go github.com/mattermost/mattermost-server
Go github.com/mattermost/mattermost/server/v8
Go github.com/mattermost/mattermost-server
Go github.com/mattermost/mattermost-server/v5
Go github.com/mattermost/mattermost-server/v6
Go github.com/mattermost/mattermost/server/v8

03 / CONNECTIONS

Connected vulnerabilities

related OPENSUSE-SU-2026:21483-1

04 / EVIDENCE

Source records

Open Source Vulnerabilities CVE-2026-25783

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

View original source
Open Source Vulnerabilities GHSA-2v3w-6g35-5f9v

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

View original source
Open Source Vulnerabilities GO-2026-4725

Mattermost fails to properly validate User-Agent header tokens in github.com/mattermost/mattermost-server. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: github.com/mattermost/mattermost-server/v5 before v5.3.2-0.20260129181235-1346cf529aef.

View original source

05 / REFERENCES

Further evidence