EUVD-2026-16162Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Primary rating from NVD.
CVSS VectorNVD
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Lifecycle Timeline
4DescriptionCVE.org
Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel via sending crafted membership sync messages that trigger team membership assignment. Mattermost Advisory ID: MMSA-2026-00574
AnalysisAI
Mattermost versions 11.2.x through 11.2.2, 10.11.x through 10.11.10, 11.4.0, and 11.3.x through 11.3.1 fail to properly restrict team-level access during remote cluster membership synchronization, allowing a malicious remote cluster to grant users access to entire private teams rather than limiting access to only shared channels. An authenticated attacker controlling a federated remote cluster can send crafted membership sync messages to trigger unintended team membership assignment, resulting in unauthorized access to private team resources. The EPSS score of 0.03% (percentile 7%) indicates low real-world exploitation probability, and no public exploit code has been identified at time of analysis.
Technical ContextAI
The vulnerability exists in Mattermost's cluster federation and shared channel membership synchronization mechanism (CPE: cpe:2.3:a:mattermost:mattermost). When processing membership sync messages from remote clusters, Mattermost fails to enforce proper access control boundaries between shared channel membership and team-level membership, classified under CWE-863 (Incorrect Authorization). The root cause is inadequate validation of membership scope during the sync operation-the system does not verify that remote cluster membership changes are restricted to the intended shared channel context before applying them at the team level, allowing scope escalation from channel to team.
RemediationAI
Upgrade affected Mattermost instances to patched versions: 11.2.3 or later for the 11.2.x branch, 10.11.11 or later for the 10.11.x branch, 11.3.2 or later for the 11.3.x branch, and 11.5.0 or later for the 11.4.x branch (consult vendor advisory for exact version mapping). Until patching is feasible, restrict federation to trusted remote clusters only and implement network-level isolation of cluster-to-cluster communication channels. Review and audit existing shared channel memberships across federated clusters to identify any unauthorized team-level access grants. Enable logging and monitoring of membership sync operations to detect anomalous membership changes. See https://mattermost.com/security-updates for complete patch details and migration guidance.
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View allVendor StatusVendor
Debian
Bug #823556| Release | Status | Fixed Version | Urgency |
|---|---|---|---|
| open | - | - |
SUSE
Severity: Moderate| Product | Status |
|---|---|
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Affected |
| openSUSE Leap 15.5 | Affected |
| openSUSE Leap 15.6 | Affected |
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External POC / Exploit Code
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