CVE-2026-0999Network attack vector

SSO restriction bypass via userID authentication

Published Feb 16, 2026 · Updated Feb 16, 2026

Authentication bypass in Mattermost allows remote authenticated users to evade SSO-only login restrictions through userID-based authentication. The login flow accepts userID-based authentication without enforcing the configuration that disables email and username login in favor of SSO. An existing account is required, and the bypass permits an alternative login path rather than administrative access or code execution.

CVSS severity5.4
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Mattermost allows remote authenticated users to evade SSO-only login restrictions through userID-based authentication. The login flow accepts userID-based authentication without enforcing the configuration that disables email and username login in favor of SSO. An existing account is required, and the bypass permits an alternative login path rather than administrative access or code execution.

The record

CVE
CVE-2026-0999
Published
Feb 16, 2026
Updated
Feb 16, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-303, T1078
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 16, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 16, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.11.0 <=10.11.9
  2. Affected versionversion=11.1.0 <=11.1.2
  3. Affected versionversion=11.2.0 <=11.2.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=10.11.0 <=10.11.9; version=11.1.0 <=11.1.2; version=11.2.0 <=11.2.1

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
5.4Mattermost, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-303Incorrect Implementation of Authentication Algorithm
T1078Valid Accounts

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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