CVE-2026-18551Mattermost guest account privilege escalation via member roles API
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No exploitation reported and no EPSS estimate yet.
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Free account, 1 product
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752
- CVSS
- 6.5 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N
- Weakness (CWE)
- CWE-863
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Mattermost
- NVD analysis
- Awaiting Analysis
- Record last updated
- Oct 17, 2026
- First seen by InfoSec Signals
- Oct 16, 2026
Affected products
Mattermost Mattermost mattermost:mattermost (from the name) | from 11.10.0 through 11.10.0; from 11.7.0 through 11.7.9; from 11.9.0 through 11.9.1; from 11.8.0 through 11.8.5; 11.11.0 not affected; 11.10.1 not affected; 11.7.10 not affected; 11.9.2 not affected; and 1 more ranges | CNA record |
References
- https://mattermost.com/security-updatesvendor-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.