What is the CVSS score of CVE-2026-0999?

CVE-2026-0999 has a CVSS 3.1 base score of 5.4 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N. EPSS exploitation probability: 0.0%.

Which versions of Mattermost Server are affected by CVE-2026-0999?

CVE-2026-0999 presents moderate security risk rated CVSS 5.4. Exploitation could compromise the security of affected deployments.. A patch is available.

How to fix or mitigate CVE-2026-0999?

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.

Mattermost Server CVE-2026-0999

MEDIUM

Incorrect Implementation of Authentication Algorithm (CWE-303)

2026-02-16 responsibledisclosure@mattermost.com

Authentication Bypass Mattermost Server Suse

5.4

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

5.4 MEDIUM

AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

SUSE

MEDIUM

qualitative

Primary rating from NVD.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

None

Lifecycle Timeline

Patch released

Mar 31, 2026 - 21:13 nvd

Patch available

Analysis Generated

Mar 12, 2026 - 21:54 vuln.today

CVE Published

Feb 16, 2026 - 10:16 nvd

MEDIUM 5.4

DescriptionCVE.org

Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to properly validate login method restrictions which allows an authenticated user to bypass SSO-only login requirements via userID-based authentication. Mattermost Advisory ID: MMSA-2025-00548

AnalysisAI

Mattermost Server versions 11.1.x through 11.1.2, 10.11.x through 10.11.9, and 11.2.x through 11.2.1 inadequately enforce login method restrictions, permitting authenticated users to circumvent SSO-only requirements by authenticating with a userID instead. This allows an attacker with valid credentials to gain unauthorized access to accounts restricted to single sign-on authentication. No patch is currently available for this vulnerability.

Technical ContextAI

Affects Mattermost Server. Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to properly validate login method restrictions which allows an authenticated user to bypass SSO-only login requirements via userID-based authentication. Mattermost Advisory ID: MMSA-2025-00548

RemediationAI

Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.

More in Mattermost Server

View all

CVE-2025-25279 CRITICAL Act Now

9.9 Feb 24

Mattermost versions 10.4.x <= 10.4.1, 9.11.x <= 9.11.7, 10.3.x <= 10.3.2, 10.2.x <= 10.2.2 fail to properly validate boa

CVE-2022-3257 MEDIUM This Month POC

6.5 Sep 23

Mattermost version 7.1.x and earlier fails to sufficiently process a specifically crafted GIF file when it is uploaded w

CVE-2025-4981 CRITICAL Act Now

9.9 Jun 20

A remote code execution vulnerability (CVSS 9.9) that allows authenticated users. Critical severity with potential for s

CVE-2025-20051 CRITICAL Act Now

9.9 Feb 24

Mattermost versions 10.4.x <= 10.4.1, 9.11.x <= 9.11.7, 10.3.x <= 10.3.2, 10.2.x <= 10.2.2 fail to properly validate inp

CVE-2025-12421 CRITICAL Act Now

9.9 Nov 27

Mattermost versions 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to to verify that t

CVE-2025-12419 CRITICAL Act Now

9.9 Nov 27

Mattermost versions 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12, 11.0.x <= 11.0.3 fail to properly validat

CVE-2023-6458 CRITICAL Act Now

9.8 Dec 06

Mattermost webapp fails to validate route parameters in/<TEAM_NAME>/channels/<CHANNEL_NAME> allowing an attacker to perf

CVE-2025-24490 CRITICAL Act Now

9.6 Feb 24

Mattermost versions 10.4.x <= 10.4.1, 9.11.x <= 9.11.7, 10.3.x <= 10.3.2, 10.2.x <= 10.2.2 fail to use prepared statemen

CVE-2024-2450 HIGH This Week

8.8 Mar 15

Mattermost versions 8.1.x before 8.1.10, 9.2.x before 9.2.6, 9.3.x before 9.3.2, and 9.4.x before 9.4.3 fail to correctl

CVE-2023-45316 HIGH This Week

8.8 Dec 12

Mattermost fails to validate if a relative path is passed in /plugins/playbooks/api/v0/telemetry/run/<telem_run_id> as a

CVE-2023-2515 HIGH This Week

8.8 May 12

Mattermost fails to restrict a user with permissions to edit other users and to create personal access tokens from eleva

CVE-2022-1384 HIGH This Week

8.8 Apr 19

Mattermost version 6.4.x and earlier fails to properly check the plugin version when a plugin is installed from the Mark

Same weakness CWE-303 – Incorrect Implementation of Authentication Algorithm

View all

CVE-2023-29357 CRITICAL POC

9.8

CVE-2025-13390 CRITICAL POC

10.0

CVE-2025-66489 CRITICAL POC

9.8

CVE-2026-28446 CRITICAL POC

9.4

CVE-2025-57808 HIGH POC

8.1

CVE-2016-9463 HIGH POC

8.1

CVE-2026-43640 HIGH POC

8.6

CVE-2025-44557 HIGH POC

8.1

Same technique Authentication Bypass

View all

CVE-2023-22515 CRITICAL POC

9.8

CVE-2012-4681 CRITICAL POC

9.8

CVE-2013-2465 CRITICAL POC

9.8

CVE-2011-3544 CRITICAL POC

9.8

CVE-2012-1723 CRITICAL POC

9.8

CVE-2017-10271 HIGH POC

7.5

CVE-2015-1427 CRITICAL POC

9.8

CVE-2025-3248 CRITICAL POC

9.8

Vendor StatusVendor

SUSE

Severity: Medium

Product	Status
openSUSE Leap 15.6	Fixed
SUSE Linux Enterprise Module for Package Hub 15 SP5	Fixed
SUSE Linux Enterprise Module for Package Hub 15 SP6	Fixed
openSUSE Leap 15.5	Fixed

CVE-2026-0999 vulnerability details – vuln.today

Back

Mattermost Server CVE-2026-0999

Severity by source

CVSS VectorNVD

Lifecycle Timeline

DescriptionCVE.org

AnalysisAI

Technical ContextAI

RemediationAI

More in Mattermost Server

Same weakness CWE-303 – Incorrect Implementation of Authentication Algorithm

Same technique Authentication Bypass

Vendor StatusVendor

SUSE

Share

External POC / Exploit Code