CVE-2026-15754 PUBLISHED

Missing per-channel team-scope check in ABAC access control policy unassign allows cross-team policy removal

Assigner: Mattermost
Reserved: 14.07.2026 Published: 17.08.2026 Updated: 17.08.2026

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

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:H/A:N
CVSS Score: 4.2

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	None
Privileges Required	High	Integrity Impact	High
User Interaction	Required	Availability Impact	None

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.7.0 to 11.7.6 (incl.) affected from 11.8.0 to 11.8.3 (incl.) Version 11.9.0 is unaffected Version 11.7.7 is unaffected Version 11.8.4 is unaffected

Solutions

Update Mattermost to versions 11.9.0, 11.7.7, 11.8.4 or higher.

Credits

KennySki finder

References

MMSA-2026-00718

Problem Types

CWE-863: Incorrect Authorization CWE