CVE-2026-21386

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-21386", "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "state": "PUBLISHED", "assignerShortName": "Mattermost", "dateReserved": "2026-02-13T10:01:31.918Z", "datePublished": "2026-03-16T14:51:43.263Z", "dateUpdated": "2026-03-16T18:39:14.064Z"}, "containers": {"cna": {"affected": [{"defaultStatus": "unaffected", "product": "Mattermost", "vendor": "Mattermost", "versions": [{"lessThanOrEqual": "11.3.0", "status": "affected", "version": "11.3.0", "versionType": "semver"}, {"lessThanOrEqual": "11.2.2", "status": "affected", "version": "11.2.0", "versionType": "semver"}, {"lessThanOrEqual": "10.11.10", "status": "affected", "version": "10.11.0", "versionType": "semver"}, {"version": "11.4.0", "status": "unaffected"}, {"version": "11.3.1", "status": "unaffected"}, {"version": "11.2.3", "status": "unaffected"}, {"version": "10.11.11", "status": "unaffected"}]}], "credits": [{"lang": "en", "type": "finder", "value": "winfunc"}], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588"}], "metrics": [{"cvssV3_1": {"attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "NONE", "availabilityImpact": "NONE", "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N", "baseSeverity": "MEDIUM", "baseScore": 4.3}, "format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "description": "CWE-203: Observable Discrepancy", "cweId": "CWE-203"}]}], "references": [{"url": "https://mattermost.com/security-updates", "name": "MMSA-2026-00588", "tags": ["vendor-advisory"]}], "solutions": [{"value": "Update Mattermost to versions 11.4.0, 11.3.1, 11.2.3, 10.11.11 or higher.", "lang": "en"}], "source": {"advisory": "MMSA-2026-00588", "defect": ["https://mattermost.atlassian.net/browse/MM-67278"], "discovery": "EXTERNAL"}, "title": "Private channel enumeration via /mute slash command", "providerMetadata": {"orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "shortName": "Mattermost", "dateUpdated": "2026-03-16T14:51:43.263Z"}, "x_generator": {"engine": "cvelib 1.8.0"}}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-03-16T18:39:00.239699Z", "id": "CVE-2026-21386", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "partial"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-03-16T18:39:14.064Z"}}]}}

{"dataType": "CVE_RECORD", "containers": {"adp": [{"title": "CISA ADP Vulnrichment", "metrics": [{"other": {"type": "ssvc", "content": {"id": "CVE-2026-21386", "role": "CISA Coordinator", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "partial"}], "version": "2.0.3", "timestamp": "2026-03-16T18:39:00.239699Z"}}}], "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-03-16T18:39:06.523Z"}}], "cna": {"title": "Private channel enumeration via /mute slash command", "source": {"defect": ["https://mattermost.atlassian.net/browse/MM-67278"], "advisory": "MMSA-2026-00588", "discovery": "EXTERNAL"}, "credits": [{"lang": "en", "type": "finder", "value": "winfunc"}], "metrics": [{"format": "CVSS", "cvssV3_1": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 4.3, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "LOW", "confidentialityImpact": "LOW"}, "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "affected": [{"vendor": "Mattermost", "product": "Mattermost", "versions": [{"status": "affected", "version": "11.3.0", "versionType": "semver", "lessThanOrEqual": "11.3.0"}, {"status": "affected", "version": "11.2.0", "versionType": "semver", "lessThanOrEqual": "11.2.2"}, {"status": "affected", "version": "10.11.0", "versionType": "semver", "lessThanOrEqual": "10.11.10"}, {"status": "unaffected", "version": "11.4.0"}, {"status": "unaffected", "version": "11.3.1"}, {"status": "unaffected", "version": "11.2.3"}, {"status": "unaffected", "version": "10.11.11"}], "defaultStatus": "unaffected"}], "solutions": [{"lang": "en", "value": "Update Mattermost to versions 11.4.0, 11.3.1, 11.2.3, 10.11.11 or higher."}], "references": [{"url": "https://mattermost.com/security-updates", "name": "MMSA-2026-00588", "tags": ["vendor-advisory"]}], "x_generator": {"engine": "cvelib 1.8.0"}, "descriptions": [{"lang": "en", "value": "Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588"}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "cweId": "CWE-203", "description": "CWE-203: Observable Discrepancy"}]}], "providerMetadata": {"orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "shortName": "Mattermost", "dateUpdated": "2026-03-16T14:51:43.263Z"}}}, "cveMetadata": {"cveId": "CVE-2026-21386", "state": "PUBLISHED", "dateUpdated": "2026-03-16T18:39:14.064Z", "dateReserved": "2026-02-13T10:01:31.918Z", "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "datePublished": "2026-03-16T14:51:43.263Z", "assignerShortName": "Mattermost"}, "dataVersion": "5.2"}

{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Mattermost", "vendor": "Mattermost", "versions": [{"lessThanOrEqual": "11.3.0", "status": "affected", "version": "11.3.0", "versionType": "semver"}, {"lessThanOrEqual": "11.2.2", "status": "affected", "version": "11.2.0", "versionType": "semver"}, {"lessThanOrEqual": "10.11.10", "status": "affected", "version": "10.11.0", "versionType": "semver"}, {"status": "unaffected", "version": "11.4.0"}, {"status": "unaffected", "version": "11.3.1"}, {"status": "unaffected", "version": "11.2.3"}, {"status": "unaffected", "version": "10.11.11"}]}], "source": "responsibledisclosure@mattermost.com"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "matchCriteriaId": "B6E5F368-358C-429B-8F04-3C8DF4A71A91", "versionEndExcluding": "10.11.11", "versionStartIncluding": "10.11.0", "vulnerable": true}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "matchCriteriaId": "7F64C167-943D-4F3F-9374-BCC8DECB3881", "versionEndExcluding": "11.2.3", "versionStartIncluding": "11.2.0", "vulnerable": true}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "matchCriteriaId": "945A6E29-209F-4992-8692-BEF63DCB6B98", "versionEndExcluding": "11.3.1", "versionStartIncluding": "11.3.0", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588"}, {"lang": "es", "value": "Las versiones de Mattermost 11.3.x &lt;= 11.3.0, 11.2.x &lt;= 11.2.2, 10.11.x &lt;= 10.11.10 no utilizan respuestas de error consistentes al manejar el comando /mute, lo que permite a un miembro del equipo autenticado enumerar canales privados sobre los que no est\u00e1n autorizados a conocer, a trav\u00e9s de mensajes de error diferentes para canales inexistentes frente a canales privados. ID de Aviso de Mattermost: MMSA-2026-00588"}], "id": "CVE-2026-21386", "lastModified": "2026-06-17T10:18:36.787", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 4.3, "baseSeverity": "MEDIUM", "confidentialityImpact": "LOW", "integrityImpact": "NONE", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N", "version": "3.1"}, "exploitabilityScore": 2.8, "impactScore": 1.4, "source": "responsibledisclosure@mattermost.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-21386", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-03-16T18:39:00.239699Z", "version": "2.0.3"}}]}, "published": "2026-03-16T15:16:20.927", "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-203"}], "source": "responsibledisclosure@mattermost.com", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[11.3.0,11.3.0]"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[11.2.0,11.2.2]"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[10.11.0,10.11.10]"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.4.0"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.3.1"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.2.3"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "10.11.11"}}], "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": "2026-03-18T15:38:36.900147+00:00", "value": {"mitigation_remediation": ["Apply the vendor\u2011supplied patch by upgrading to Mattermost 11.4.0, 11.3.1, 11.2.3, or 10.11.11 or newer.", "Verify that the upgrade succeeded by checking the running Mattermost version.", "If an immediate upgrade is not possible, plan the update for the next maintenance window and monitor Mattermost security advisories for further guidance."], "summary": {"action": "Immediate Patch", "impact": "Information Disclosure"}, "threat_synthesis": {"affected_systems": "The vulnerability affects Mattermost server deployments running any version 11.3.x that is less than or equal to 11.3.0, any 11.2.x version up to 11.2.2 inclusive, or any 10.11.x version up to 10.11.10 inclusive; newer releases such as 11.4.0, 11.3.1, 11.2.3, and 10.11.11 are not affected.", "description_and_impact": "Mattermost versions 11.3.0, 11.2.0\u201311.2.2 and 10.11.0\u201310.11.10 fail to use consistent error responses when processing the /mute slash command. This flaw allows an authenticated team member to distinguish between channels that do not exist and channels that are private and inaccessible, thereby enumerating the existence of private channels. The weakness is an information disclosure flaw (CWE\u2011203).", "risk_and_exploitability": "The CVSS score of 4.3 indicates moderate severity. The EPSS score is below\u202f1\u202f%, suggesting a low likelihood of exploitation in the wild. The vulnerability is not listed in the CISA KEV catalog. Exploitation requires an authenticated user in the same Mattermost team and releases differing error messages depending on channel existence, so the attack vector is internal. No remote or unauthenticated exploitation is described."}}}}, "created": "2026-03-17T09:52:44.859137+00:00", "updated": "2026-03-24T10:44:19.009076+00:00", "vendors": ["mattermost", "mattermost$PRODUCT$mattermost"]}