{"id":"CVE-2026-25783","aliases":["GHSA-2v3w-6g35-5f9v","GO-2026-4725"],"url":"https://o3.security/vulnerability/CVE-2026-25783","summary":"Denial of service via malformed User-Agent header in getBrowserVersion","details":"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","published":"2026-03-16T12:04:18.478Z","modified":"2026-09-18T03:46:20.711967331Z","cvss":{"score":4.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L"},"epss":{"score":0.00285,"percentile":0.21159,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","fixedVersion":"8.0.0-20260129181235-1346cf529aef"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"5.3.2-0.20260129181235-1346cf529aef"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"10.11.11"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"11.2.3"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"11.3.1"}],"fix":{"url":"https://github.com/mattermost/mattermost/commit/1346cf529aef0672c39a56ec10d1b8a9c8fb387d","label":"mattermost/mattermost@1346cf5"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/25xxx/CVE-2026-25783.json"},{"type":"ADVISORY","url":"https://mattermost.com/security-updates"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-25783"},{"type":"WEB","url":"https://github.com/mattermost/mattermost/commit/1346cf529aef0672c39a56ec10d1b8a9c8fb387d"},{"type":"PACKAGE","url":"https://github.com/mattermost/mattermost"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-18T03:46:20.711967331Z"}}