# CVE-2026-4274: Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access

> CVE-2026-4274: Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access. CVSS 5.4 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-4274
Last updated: 2026-06-17T10:56:20Z

- Published: 2026-03-26 10:43 UTC · Updated: 2026-06-17 10:56 UTC · Assigner: Mattermost
- CVSS: 5.4 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
- EPSS: 0.14%, 4th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-863

## Description

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

## Affected vendors and products

- Mattermost: Mattermost

## Tracked companies

- [Mattermost](https://rewindex.com/company/mattermost.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-4274)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-4274)
- [https://mattermost.com/security-updates](https://mattermost.com/security-updates)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-4274 · Markdown: https://rewindex.com/cve/CVE-2026-4274.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-4274 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:13:32.854Z