CVE-2026-27656 (GCVE-0-2026-27656)

Vulnerability from cvelistv5 – Published: 2026-03-25 16:28 – Updated: 2026-03-26 13:19
VLAI?
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)
CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:N
CWE
  • CWE-303 - Incorrect Implementation of Authentication Algorithm
Assigner
References
Impacted products
Vendor Product Version
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
Create a notification for this product.
Credits
Christopher Poile
Show details on NVD website
To clipboard 

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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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