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… (CVE-2026-16047)
Mattermost versions 11.7.x up to 11.7.6, 10.11.x up to 10.11.21, and 11.8.x up to 11.8.3 contain a vulnerability where the software fails to verify that users have read access to a channel before linking a board to it. This flaw allows an authenticated attacker to discover membership of private channels within the same team by manipulating boards with arbitrary channel IDs.
AI Analysis
Technical Summary
CVE-2026-16047 affects Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, and 11.8.x <= 11.8.3. The vulnerability arises from improper access control validation when linking boards to channels. Specifically, the application does not confirm that a user has read permissions for a channel before allowing the creation, patching, importing, or bulk-creation of boards referencing that channel. This enables an authenticated user to infer membership of private channels on the same team by associating boards with arbitrary channel IDs.
Potential Impact
An authenticated attacker can discover membership information of private channels within the same team, potentially exposing sensitive user membership data. The vulnerability does not allow modification or denial of service but leaks confidential membership information. The CVSS v3.1 base score is 4.3 (medium severity), reflecting low confidentiality impact, no integrity or availability impact, and requiring low attack complexity with privileges.
Mitigation Recommendations
No official patch or fix information is provided in the advisory. Patch status is not yet confirmed — check the Mattermost vendor advisory MMSA-2026-00674 for current remediation guidance. Until a fix is available, restrict access to Mattermost instances to trusted users and monitor for suspicious activity related to board creation or linking. Avoid granting unnecessary permissions that allow board creation or modification to reduce risk.
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… (CVE-2026-16047)
Description
Mattermost versions 11.7.x up to 11.7.6, 10.11.x up to 10.11.21, and 11.8.x up to 11.8.3 contain a vulnerability where the software fails to verify that users have read access to a channel before linking a board to it. This flaw allows an authenticated attacker to discover membership of private channels within the same team by manipulating boards with arbitrary channel IDs.
CVSS v3.1
Score 4.3medium
Affected software
pkg:github/mattermost/mattermost-serverRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-16047 affects Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, and 11.8.x <= 11.8.3. The vulnerability arises from improper access control validation when linking boards to channels. Specifically, the application does not confirm that a user has read permissions for a channel before allowing the creation, patching, importing, or bulk-creation of boards referencing that channel. This enables an authenticated user to infer membership of private channels on the same team by associating boards with arbitrary channel IDs.
Potential Impact
An authenticated attacker can discover membership information of private channels within the same team, potentially exposing sensitive user membership data. The vulnerability does not allow modification or denial of service but leaks confidential membership information. The CVSS v3.1 base score is 4.3 (medium severity), reflecting low confidentiality impact, no integrity or availability impact, and requiring low attack complexity with privileges.
Mitigation Recommendations
No official patch or fix information is provided in the advisory. Patch status is not yet confirmed — check the Mattermost vendor advisory MMSA-2026-00674 for current remediation guidance. Until a fix is available, restrict access to Mattermost instances to trusted users and monitor for suspicious activity related to board creation or linking. Avoid granting unnecessary permissions that allow board creation or modification to reduce risk.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-7xj3-8pxr-p8pc
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-16047"]
- Ecosystems
- []
- Database Specific Severity
- MODERATE
- Cvss Version
- 3.1
Threat ID: 6a833345bf8831d5392a3c74
Added to database: 08/17/2026, 16:13:57 UTC
Last enriched: 08/17/2026, 16:17:08 UTC
Last updated: 08/17/2026, 19:01:11 UTC
Views: 3
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