Mattermost up to 10.11.9/11.1.2/11.2.1 Login incorrect implementation of authentication algorithm

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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5.2$0-$5k0.00

Summaryinfo

A vulnerability classified as critical was found in Mattermost up to 10.11.9/11.1.2/11.2.1. This affects an unknown function of the component Login. Such manipulation leads to incorrect implementation of authentication algorithm. This vulnerability is listed as CVE-2026-0999. The attack may be performed from remote. There is no available exploit. Upgrading the affected component is advised.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Mattermost up to 10.11.9/11.1.2/11.2.1. Affected by this issue is an unknown function of the component Login. The manipulation with an unknown input leads to a incorrect implementation of authentication algorithm vulnerability. Using CWE to declare the problem leads to CWE-303. The requirements for the product dictate the use of an established authentication algorithm, but the implementation of the algorithm is incorrect. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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

The weakness was presented by daw10. The advisory is available at mattermost.com. This vulnerability is handled as CVE-2026-0999 since 01/15/2026. The exploitation is known to be easy. The attack may be launched remotely. The technical details are unknown and an exploit is not available.

Upgrading to version 10.11.10, 11.1.3, 11.2.2 or 11.3.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-6102). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Type

Name

Version

License

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.3
VulDB Meta Temp Score: 5.2

VulDB Base Score: 6.3
VulDB Temp Score: 6.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 4.3
NVD Vector: 🔒

CNA Base Score: 5.4
CNA Vector (Mattermost): 🔒

CVSSv2info

AVACAuCIA
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💳💳💳💳💳💳
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Incorrect implementation of authentication algorithm
CWE: CWE-303
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Mattermost 10.11.10/11.1.3/11.2.2/11.3.0

Timelineinfo

01/15/2026 CVE reserved
02/16/2026 +32 days Advisory disclosed
02/16/2026 +0 days VulDB entry created
02/20/2026 +4 days VulDB entry last update

Sourcesinfo

Advisory: mattermost.com
Researcher: daw10
Status: Confirmed

CVE: CVE-2026-0999 (🔒)
GCVE (CVE): GCVE-0-2026-0999
GCVE (VulDB): GCVE-100-346178
EUVD: 🔒

Entryinfo

Created: 02/16/2026 11:26
Updated: 02/20/2026 08:22
Changes: 02/16/2026 11:26 (64), 02/18/2026 05:50 (1), 02/20/2026 08:22 (12)
Complete: 🔍
Cache ID: 216::103

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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