{"id":"CVE-2026-26233","state":"PUBLISHED","title":"Denial of Service via HTTP/2 single packet attack on login endpoint","description":"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","publishedAt":"2026-03-25T16:24:47.694Z","updatedAt":"2026-03-27T14:59:50.732Z","severity":{"score":4.3,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","source":"Mattermost"},"assigner":"Mattermost","products":["Mattermost Mattermost"],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.4.0","status":"affected","lessThanOrEqual":"11.4.0","versionType":"semver"},{"version":"11.3.0","status":"affected","lessThanOrEqual":"11.3.1","versionType":"semver"},{"version":"11.2.0","status":"affected","lessThanOrEqual":"11.2.3","versionType":"semver"},{"version":"10.11.0","status":"affected","lessThanOrEqual":"10.11.11","versionType":"semver"},{"version":"11.5.0","status":"unaffected"},{"version":"11.4.1","status":"unaffected"},{"version":"11.3.2","status":"unaffected"},{"version":"11.2.4","status":"unaffected"},{"version":"10.11.12","status":"unaffected"}]}],"references":["https://mattermost.com/security-updates"],"weaknesses":["CWE-400"],"ingestedAt":"2026-10-29T20:11:21.040Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/26xxx/CVE-2026-26233.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-26233","state":"PUBLISHED","datePublished":"2026-03-25T16:24:47.694Z","dateUpdated":"2026-03-27T14:59:50.732Z","assignerShortName":"Mattermost","assignerOrgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateReserved":"2026-02-23T22:18:41.232Z"},"containers":{"cna":{"title":"Denial of Service via HTTP/2 single packet attack on login endpoint","descriptions":[{"lang":"en","value":"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"}],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.4.0","status":"affected","lessThanOrEqual":"11.4.0","versionType":"semver"},{"version":"11.3.0","status":"affected","lessThanOrEqual":"11.3.1","versionType":"semver"},{"version":"11.2.0","status":"affected","lessThanOrEqual":"11.2.3","versionType":"semver"},{"version":"10.11.0","status":"affected","lessThanOrEqual":"10.11.11","versionType":"semver"},{"version":"11.5.0","status":"unaffected"},{"version":"11.4.1","status":"unaffected"},{"version":"11.3.2","status":"unaffected"},{"version":"11.2.4","status":"unaffected"},{"version":"10.11.12","status":"unaffected"}]}],"references":[{"url":"https://mattermost.com/security-updates","name":"MMSA-2025-00566","tags":["vendor-advisory"]}],"metrics":[{"cvssV3_1":{"attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"LOW","version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","baseSeverity":"MEDIUM","baseScore":4.3},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-400","lang":"en","type":"CWE","description":"CWE-400 Uncontrolled Resource Consumption"}]}],"providerMetadata":{"shortName":"Mattermost","orgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateUpdated":"2026-03-25T16:24:47.694Z"},"credits":[{"lang":"en","type":"finder","value":"Axel Larsson & Jakob Ristner"}],"solutions":[{"value":"Update Mattermost to versions 11.5.0, 11.4.1, 11.3.2, 11.2.4, 10.11.12 or higher.","lang":"en"}],"source":{"advisory":"MMSA-2025-00566","defect":["https://mattermost.atlassian.net/browse/MM-66885"],"discovery":"EXTERNAL"},"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-03-27T14:59:40.444232Z","id":"CVE-2026-26233","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-03-27T14:59:50.732Z"}}]}}}