CVE-2026-27656 (GCVE-0-2026-27656)
Vulnerability from cvelistv5 – Published: 2026-03-25 16:28 – Updated: 2026-03-26 13:19
VLAI
EPSS
VEX
Title
Account Takeover via Substring Matching in OpenID Connect Authentication
Summary
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
Severity
5.7 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-03-26 03:55 UTC
CWE
- CWE-303 - Incorrect Implementation of Authentication Algorithm
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://mattermost.com/security-updates | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Mattermost | Mattermost |
Affected:
11.4.0 , ≤ 11.4.0
(semver)
Affected: 11.3.0 , ≤ 11.3.1 (semver) Affected: 11.2.0 , ≤ 11.2.3 (semver) Affected: 10.11.0 , ≤ 10.11.11 (semver) Unaffected: 11.5.0 Unaffected: 11.4.1 Unaffected: 11.3.2 Unaffected: 11.2.4 Unaffected: 10.11.12 |
guessed |
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