Mattermost guest account privilege escalation via member roles API
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
CVE-2026-18551
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: cve:CVE-2026-18551
Mattermost
Source reference: /containers/cna/affected/0/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"vendor": "Mattermost",
"product": "Mattermost",
"versions": [
{
"status": "affected",
"version": "11.10.0",
"versionType": "semver",
"lessThanOrEqual": "11.10.0"
},
{
"status": "affected",
"version": "11.7.0",
"versionType": "semver",
"lessThanOrEqual": "11.7.9"
},
{
"status": "affected",
"version": "11.9.0",
"versionType": "semver",
"lessThanOrEqual": "11.9.1"
},
{
"status": "affected",
"version": "11.8.0",
"versionType": "semver",
"lessThanOrEqual": "11.8.5"
},
{
"status": "unaffected",
"version": "11.11.0"
},
{
"status": "unaffected",
"version": "11.10.1"
},
{
"status": "unaffected",
"version": "11.7.10"
},
{
"status": "unaffected",
"version": "11.9.2"
},
{
"status": "unaffected",
"version": "11.8.6"
}
],
"defaultStatus": "unaffected"
}
]- Related CVEs
- CVE-2026-18551
Source reference:
/cveMetadata/cveId
Publisher severity
medium
Source reference: /containers/cna/metrics
- Event
- #42160 · Revision 1
- Added to Heist Feed
- Publisher date