5.4

CVE-2026-0999: Authentication bypass via userID login when email and username login are disabled

Analyzed
AliasesGHSA-3c9r-7f29-qp32GO-2026-4520
Published 16-02-2026Last modified 17-02-2026

Vulnerability summary

CVE-2026-0999 is a medium (CVSS 5.4) vulnerability in mattermost. EPSS estimates a 0.20% chance of exploitation in the next 30 days, higher than 9.9% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 5.4, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
5.4/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.20%
0%100%
Low · +0.02 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 2 · Related 2
OPENSUSE-SU-2026:21483-1SUSE-SU-2026:0757-1

Timeline

  1. 16-02-2026
    PublishedVulnerability first disclosed.
  2. 17-02-2026
    Last modifiedVulnerability information updated.

Description

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

CVSS metrics

3 scores · 3 sources · 1 version

EPSS trend

Probability

0.20%

Chance of exploitation in the next 30 days

Percentile

10%

Versus all other CVEs

30-day change

Increase +0.02 pp

From 0.18% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.

Github.com/mattermost/mattermost-server2 products
  • v5All versions (No fix recorded)
  • v6All versions (No fix recorded)
Mattermost2 products
  • mattermost≥ 11.1.0, ≤ 11.1.2 | ≥ 10.11.0, ≤ 10.11.9 | ≥ 11.2.0, ≤ 11.2.1
  • mattermost_server≥ 10.11.0, < 10.11.10 | ≥ 11.1.0, < 11.1.3 | ≥ 11.2.0, < 11.2.2
Github.com/mattermost1 product
  • mattermost-server≥ 11.1.0 (No fix recorded) | ≥ 10.11.0 (No fix recorded) | ≥ 11.2.0 (No fix recorded) | < 5.3.2-0.20251212052346-61651b0df7ea | All versions (No fix recorded) | ≥ 10.11.0+incompatible (No fix recorded) | ≥ 11.1.0+incompatible (No fix recorded) | ≥ 11.2.0+incompatible (No fix recorded)
Github.com/mattermost/mattermost/server1 product
  • v8< 8.0.0-20251212052346-61651b0df7ea

4 vendors · 6 products

References

5 links