CVE-2026-0999
Authentication Bypass in Mattermost via Improper Login Validation
Publication date: 2026-02-16
Last updated on: 2026-02-18
Assigner: Mattermost, Inc.
Description
Description
CVSS Scores
EPSS Scores
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| Percentile: |
Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| mattermost | mattermost_server | From 10.11.0 (inc) to 10.11.10 (exc) |
| mattermost | mattermost_server | From 11.2.0 (inc) to 11.2.2 (exc) |
| mattermost | mattermost_server | From 11.1.0 (inc) to 11.1.3 (exc) |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-303 | The requirements for the product dictate the use of an established authentication algorithm, but the implementation of the algorithm is incorrect. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
This vulnerability affects certain versions of Mattermost (11.1.x up to 11.1.2, 10.11.x up to 10.11.9, and 11.2.x up to 11.2.1) where the software fails to properly validate login method restrictions.
Specifically, it allows an authenticated user to bypass Single Sign-On (SSO) only login requirements by using userID-based authentication.
How can this vulnerability impact me? :
An attacker who is already authenticated can bypass the intended SSO-only login restrictions.
This could lead to unauthorized access methods being used, potentially weakening the security posture by allowing users to authenticate in ways that were meant to be restricted.
The CVSS base score of 5.4 indicates a medium severity impact with low attack complexity and no user interaction required.
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
I don't know
How can this vulnerability be detected on my network or system? Can you suggest some commands?
I don't know
What immediate steps should I take to mitigate this vulnerability?
I don't know