CVE-2026-16047 PUBLISHED

Board channel linking without read channel permission validation

Assigner: Mattermost
Reserved: 17.07.2026 Published: 17.08.2026 Updated: 17.08.2026

Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate that users have read access to a channel before linking a board to it, which allows an authenticated attacker to discover the membership of private channels on the same team via creating, patching, importing, or bulk-creating boards with an arbitrary channelId. Mattermost Advisory ID: MMSA-2026-00674

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
CVSS Score: 4.3

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	Low
Privileges Required	Low	Integrity Impact	None
User Interaction	None	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 10.11.0 to 10.11.21 (incl.) affected from 11.8.0 to 11.8.3 (incl.) Version 11.9.0 is unaffected Version 11.7.7 is unaffected Version 10.11.22 is unaffected Version 11.8.4 is unaffected

Solutions

Update Mattermost to versions 11.9.0, 11.7.7, 10.11.22, 11.8.4 or higher.

Credits

GuyNesher finder

References

MMSA-2026-00674

Problem Types

CWE-862: Missing Authorization CWE