CVE-2026-27656

MEDIUM EPSS 7.7%
Published Mar 25, 20263mo ago · Modified Jun 17, 20262w ago
6.1 CVSS 3.1
Medium
Find Similar
Published Mar 25, 2026 3mo ago
Last Modified Jun 17, 2026 2w ago

Description

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

CVSS Details

Base Score
6.1
Exploitability
0.9
Impact
5.2
Vector string
CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N
Attack Vector Network
Attack Complexity Low
Privileges Required High
User Interaction Required
Scope Unchanged
Confidentiality High
Integrity High
Availability None

Threat Intelligence

EPSS Exploit Probability
7.7% percentile
Exploit & Patch Status
No Known Exploit
No Patch Available

Weaknesses 1

CWE-303

Affected Products 4

VendorProductVersionRange
mattermostmattermost_server*≥10.11.0  –  <10.11.12
mattermostmattermost_server*≥11.2.0  –  <11.2.4
mattermostmattermost_server*≥11.3.0  –  <11.3.2
mattermostmattermost_server*≥11.4.0  –  <11.4.1

References 1

  • mattermost.com https://mattermost.com/security-updates
    Vendor Advisory

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.