VDB
CVE-2026-27656
CVE-2026-27656
PUBLISHED
CVSS 5.699999809265137 MEDIUM
Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to properly validate user identity in the OpenID {{IsSameUser()}} comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user discovery flow.. Mattermost Advisory ID: MMSA-2026-00590
EPSS 0.04% · 11.6th percentile
Risk Scores
CVSS 3.1
5.699999809265137
CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:N
EPSS Score
0.04%
11.6th percentile
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| github.com | mattermost/mattermost-server | 10.11.0-rc1, 11.2.0-rc1, 11.3.0-rc1 |
| github.com | mattermost/mattermost/server/v8 | 8.0.0-20260105080200 |
| Mattermost | Mattermost | 11.2.4, 11.4.1, 11.3.2 |
| mattermost | mattermost_server | 11.3.0, 11.4.0, 10.11.0 |
Timeline
- Feb 24, 2026 CVE Published
- Mar 25, 2026 Coalition ESS Score
- Mar 25, 2026 PoC Published
- Mar 26, 2026 PoC Published
- Mar 26, 2026 Security Advisory
- Mar 26, 2026 CVE Updated
- May 18, 2026 EPSS Score
- May 19, 2026 EPSS Score
- May 20, 2026 EPSS Score
- May 21, 2026 EPSS Score
- May 22, 2026 EPSS Score
- May 23, 2026 EPSS Score
References
- MMSA-2026-00590 vendor-advisory
- https://mattermost.com/security-updates/ advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-27656 advisory
- https://github.com/mattermost/mattermost package