{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-26233", "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "state": "PUBLISHED", "assignerShortName": "Mattermost", "dateReserved": "2026-02-23T22:18:41.232Z", "datePublished": "2026-03-25T16:24:47.694Z", "dateUpdated": "2026-03-25T16:24:47.694Z"}, "containers": {"cna": {"affected": [{"defaultStatus": "unaffected", "product": "Mattermost", "vendor": "Mattermost", "versions": [{"lessThanOrEqual": "11.4.0", "status": "affected", "version": "11.4.0", "versionType": "semver"}, {"lessThanOrEqual": "11.3.1", "status": "affected", "version": "11.3.0", "versionType": "semver"}, {"lessThanOrEqual": "11.2.3", "status": "affected", "version": "11.2.0", "versionType": "semver"}, {"lessThanOrEqual": "10.11.11", "status": "affected", "version": "10.11.0", "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"}]}], "credits": [{"lang": "en", "type": "finder", "value": "Axel Larsson & Jakob Ristner"}], "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"}], "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": [{"lang": "en", "type": "CWE", "description": "CWE-400 Uncontrolled Resource Consumption", "cweId": "CWE-400"}]}], "references": [{"url": "https://mattermost.com/security-updates", "name": "MMSA-2025-00566", "tags": ["vendor-advisory"]}], "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"}, "title": "Denial of Service via HTTP/2 single packet attack on login endpoint", "providerMetadata": {"orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "shortName": "Mattermost", "dateUpdated": "2026-03-25T16:24:47.694Z"}, "x_generator": {"engine": "cvelib 1.8.0"}}}}

{}

{"configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "matchCriteriaId": "D144BD1D-F65C-498D-BC8A-F3D718F47F4B", "versionEndExcluding": "10.11.12", "versionStartIncluding": "10.11.0", "vulnerable": true}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "matchCriteriaId": "2E3E9B61-F003-45E4-9A04-8015A5CB8558", "versionEndExcluding": "11.2.4", "versionStartIncluding": "11.2.0", "vulnerable": true}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "matchCriteriaId": "805ECFFC-82FD-4754-AF95-32167E1D41CB", "versionEndExcluding": "11.3.2", "versionStartIncluding": "11.3.0", "vulnerable": true}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "matchCriteriaId": "839BC7B7-28DF-4125-937A-8B0D2D6893C2", "versionEndExcluding": "11.4.1", "versionStartIncluding": "11.4.0", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "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"}, {"lang": "es", "value": "Las versiones de Mattermost 11.4.x &lt;= 11.4.0, 11.3.x &lt;= 11.3.1, 11.2.x &lt;= 11.2.3, 10.11.x &lt;= 10.11.11 no aplican l\u00edmite de tasa a las solicitudes de inicio de sesi\u00f3n, lo que permite a atacantes remotos no autenticados causar denegaci\u00f3n de servicio (ca\u00edda y reinicio del servidor) mediante un ataque de paquete \u00fanico HTTP/2 con m\u00e1s de 100 solicitudes de inicio de sesi\u00f3n paralelas. ID de Aviso de Mattermost: MMSA-2025-00566"}], "id": "CVE-2026-26233", "lastModified": "2026-03-26T18:52:31.740", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "LOW", "baseScore": 4.3, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L", "version": "3.1"}, "exploitabilityScore": 2.8, "impactScore": 1.4, "source": "responsibledisclosure@mattermost.com", "type": "Secondary"}, {"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 6.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "version": "3.1"}, "exploitabilityScore": 2.8, "impactScore": 3.6, "source": "nvd@nist.gov", "type": "Primary"}]}, "published": "2026-03-25T17:16:53.143", "references": [{"source": "responsibledisclosure@mattermost.com", "tags": ["Vendor Advisory"], "url": "https://mattermost.com/security-updates"}], "sourceIdentifier": "responsibledisclosure@mattermost.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-400"}], "source": "responsibledisclosure@mattermost.com", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "11.4.0"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "11.3.0"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "11.2.0"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "10.11.0"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.5.0"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.4.1"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.3.2"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.2.4"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "10.11.12"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "Mattermost", "source": "cna", "vendor": "Mattermost"}, "product": "mattermost", "vendor": "mattermost"}], "analysis": {"en": {"generated_at": "2026-03-26T21:55:48.481110+00:00", "value": {"mitigation_remediation": ["Apply the Mattermost patch: upgrade to version 11.5.0, 11.4.1, 11.3.2, 11.2.4, 10.11.12, or later"], "summary": {"action": "Apply Patch", "impact": "Denial of Service"}, "threat_synthesis": {"affected_systems": "The affected products are Mattermost Server versions 11.4.x (\u226411.4.0), 11.3.x (\u226411.3.1), 11.2.x (\u226411.2.3), and 10.11.x (\u226410.11.11). Any installation running these releases, regardless of operating system or deployment model, is susceptible.", "description_and_impact": "Mattermost Server releases up to 11.4.0, 11.3.1, 11.2.3, and 10.11.11 do not rate\u2011limit login requests, allowing an unauthenticated attacker to send 100+ parallel HTTP/2 single\u2011packet login requests. This overwhelms the server and causes a crash with automatic restart, effectively denying service to all users and administrators. The vulnerability corresponds to CWE\u2011400, indicating a resource\u2011exhaustion weakness.", "risk_and_exploitability": "The CVSS base score of 4.3 classifies the issue as low severity, and the EPSS score of less than 1% indicates a very low likelihood of exploitation. The vulnerability is not listed in the CISA KEV catalog. An attacker only needs unauthenticated HTTP/2 traffic to the exposed login endpoint; no privileged access is required. The attack can be executed from any network that can reach the login endpoint, and the impact is the denial of service of the Mattermost service."}}}}, "created": "2026-03-25T21:46:59.265502+00:00", "updated": "2026-03-27T09:30:35.257896+00:00", "vendors": ["mattermost", "mattermost$PRODUCT$mattermost"]}