EUVD-2026-22915
GHSA-mh4x-rmrx-3hp4
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Primary rating from NVD.
CVSS VectorNVD
Lifecycle Timeline
4DescriptionCVE.org
Mattermost versions 10.11.x <= 10.11.12, 11.5.x <= 11.5.0, 11.4.x <= 11.4.2, 11.3.x <= 11.3.2 fail to enforce atomic single-use consumption of guest magic link tokens, which allows an attacker with access to a valid magic link to establish multiple independent authenticated sessions via concurrent requests.. Mattermost Advisory ID: MMSA-2026-00624
AnalysisAI
Mattermost versions 10.11.x through 10.11.12, 11.3.x through 11.3.2, 11.4.x through 11.4.2, and 11.5.0 fail to enforce atomic consumption of guest magic link tokens, allowing unauthenticated attackers to establish multiple concurrent authenticated sessions from a single valid magic link. This enables unauthorized access and potential information disclosure without requiring additional credentials or user interaction beyond intercepting or obtaining the link.
Technical ContextAI
Mattermost's guest magic link authentication mechanism is designed to generate single-use tokens for frictionless guest access. The vulnerability stems from a race condition (CWE-367: Time-of-check Time-of-use) in the token validation logic, where the server fails to atomically mark tokens as consumed before processing authentication requests. When concurrent requests are submitted with the same token, the non-atomic validation window allows multiple requests to pass validation before any is marked consumed. This affects Mattermost server versions across the 10.11, 11.3, 11.4, and 11.5 release branches, as indicated by the CPE cpe:2.3:a:mattermost:mattermost:*:*:*:*:*:*:*:*.
RemediationAI
Upgrade to Mattermost Server version 10.11.13 or later for the 10.11 branch, 11.3.3 or later for the 11.3 branch, 11.4.3 or later for the 11.4 branch, or 11.5.1 or later for the 11.5 branch. The patch implements atomic token consumption logic to prevent reuse of magic link tokens across concurrent requests. Until patching is feasible, disable or restrict guest magic link authentication in access control policies if possible, and implement rate limiting on authentication endpoints to mitigate concurrent request exploitation. Consult https://mattermost.com/security-updates for detailed patch availability and upgrade instructions.
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Same technique Information Disclosure
View allVendor StatusVendor
SUSE
Severity: Moderate| Product | Status |
|---|---|
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Affected |
| openSUSE Leap 15.5 | Affected |
| openSUSE Leap 15.6 | Affected |
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External POC / Exploit Code
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