{"id":"CVE-2026-26233","aliases":["GHSA-247x-7qw8-fp98","GO-2026-4916"],"url":"https://o3.security/vulnerability/CVE-2026-26233","summary":"Denial of Service via HTTP/2 single packet attack on login endpoint","details":"Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to rate limit login requests which allows unauthenticated remote attackers to cause denial of service (server crash and restart) via HTTP/2 single packet attack with 100+ parallel login requests.. Mattermost Advisory ID: MMSA-2025-00566","published":"2026-03-25T16:24:47.694Z","modified":"2026-07-31T18:30:33.230993608Z","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":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"11.4.1"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"11.3.2"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"11.2.4"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"10.11.12"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/26xxx/CVE-2026-26233.json"},{"type":"ADVISORY","url":"https://mattermost.com/security-updates"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-26233"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-31T18:30:33.230993608Z"}}