CVE-2026-15754

Mattermost versions 11.7.x <= 11.7.6, 11.8.x <= 11.8.3 The access control policy unassign endpoint fails to re-validate that each target channel still belongs to the requesting admin's team, which allows an authenticated team administrator to remove ABAC (attribute-based access control) policy assignments from channels outside their team via the policy unassign API after a channel has been moved to another team.. Mattermost Advisory ID: MMSA-2026-00718

CVSS v3 4.2 MEDIUM

4.2^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 0.5 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required HIGH

User Interaction REQUIRED

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://mattermost.com/security-updates	Vendor Advisory

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:mattermost:mattermost_server::::::::
	cpe:2.3:a:mattermost:mattermost_server::::::::

History

No history.

Information

Published : 2026-08-17 15:16

Updated : 2026-08-18 20:24

NVD link : CVE-2026-15754

Mitre link : CVE-2026-15754

CVE.ORG link : CVE-2026-15754

JSON object : View

Products Affected

mattermost

mattermost_server

CWE

CWE-863

Incorrect Authorization

{"id": "CVE-2026-15754", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-15754", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-08-17T14:50:36.703223Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "responsibledisclosure@mattermost.com", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 4.2, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:H/A:N", "integrityImpact": "HIGH", "userInteraction": "REQUIRED", "attackComplexity": "HIGH", "availabilityImpact": "NONE", "privilegesRequired": "HIGH", "confidentialityImpact": "NONE"}, "impactScore": 3.6, "exploitabilityScore": 0.5}]}, "affected": [{"source": "responsibledisclosure@mattermost.com", "affectedData": [{"vendor": "Mattermost", "product": "Mattermost", "versions": [{"status": "affected", "version": "11.7.0", "versionType": "semver", "lessThanOrEqual": "11.7.6"}, {"status": "affected", "version": "11.8.0", "versionType": "semver", "lessThanOrEqual": "11.8.3"}, {"status": "unaffected", "version": "11.9.0"}, {"status": "unaffected", "version": "11.7.7"}, {"status": "unaffected", "version": "11.8.4"}], "defaultStatus": "unaffected"}]}], "published": "2026-08-17T15:16:53.743", "references": [{"url": "https://mattermost.com/security-updates", "tags": ["Vendor Advisory"], "source": "responsibledisclosure@mattermost.com"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "responsibledisclosure@mattermost.com", "description": [{"lang": "en", "value": "CWE-863"}]}], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.7.x <= 11.7.6, 11.8.x <= 11.8.3 The access control policy unassign endpoint fails to re-validate that each target channel still belongs to the requesting admin's team, which allows an authenticated team administrator to remove ABAC (attribute-based access control) policy assignments from channels outside their team via the policy unassign API after a channel has been moved to another team.. Mattermost Advisory ID: MMSA-2026-00718"}], "lastModified": "2026-08-18T20:24:58.563", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "DA4EEA22-A3E7-43AF-91F7-4B597F944100", "versionEndExcluding": "11.7.7", "versionStartIncluding": "11.7.0"}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "DE5EDDAA-76F1-4449-91BB-AFE517AD7B55", "versionEndExcluding": "11.8.4", "versionStartIncluding": "11.8.0"}], "operator": "OR"}]}], "sourceIdentifier": "responsibledisclosure@mattermost.com"}