Medium severity · published Aug 17, 2026
CVE-2026-15754
Missing per-channel team-scope check in ABAC access control policy unassign allows cross-team policy removal
4.2
CVSS
0.2%
EPSS
No
On KEV
Description
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 vector
CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:H/A:N
Attack vector
Network
Complexity
High
Privileges
High
User interaction
Required
Confidentiality
None
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 16% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.7.0 through 11.7.6; 11.8.0 through 11.8.3 · source: vendor
MS
Mattermost Server · Mattermost
11.7.0 before 11.7.7; 11.8.0 before 11.8.4 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-15754
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-15754
Vendor Advisory
https://mattermost.com/security-updates
More from Mattermost
9.9
CVE-2026-4858
Path traversal in integration action URL leading to arbitrary API execution via system admin’s auth token.
9.6
CVE-2024-39777
Mattermost versions 9.9.x <= 9.9.0, 9.5.x <= 9.5.6, 9.7.x <= 9.7.5 and 9.8.x <= 9.8.1 fail to disallow unsolicited invites to expose access to local channels, when shared channels…
9.3
CVE-2026-12985
Mattermost DCR redirect URI allowlist bypass via improper URL component validation
9.1
CVE-2023-2193
Mattermost fails to invalidate existing authorization codes when deauthorizing an OAuth2 app, allowing an attacker possessing an authorization code to generate an access token
9.1
CVE-2019-20851
An issue was discovered in Mattermost Mobile Apps before 1.26.0