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Fencer Intel
medium 5.4

CVE-2026-0999 json

Authentication bypass via userID login when email and username login are disabled

published 8mo ago modified 4mo ago also GHSA-3c9r-7f29-qp32 , GO-2026-4520 , EUVD-2026-6102

cvss
5.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 9%
public exploits
0
none known

Summary

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

Patch / fix

  • go github.com/mattermost/mattermost/server/v8 8.0.0-20251212052346-61651b0df7ea
  • go github.com/mattermost/mattermost-server 5.3.2-0.20251212052346-61651b0df7ea
  • Mattermost Mattermost 10.11.10, 11.1.3, 11.2.2, 11.3.0
  • govulncheck-vulndb openSUSE Leap 15.6 0.0.20260226T182644-150000.1.149.1

suse advisories SUSE-SU-2026:0757-1

  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

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CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
8mo ago

Exploit prediction

0.20% chance of exploitation in the next 30 days, higher than 9% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
NVD 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
GitHub 3.1 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
go github.com/mattermost/mattermost/server/v8
<8.0.0-20251212052346-61651b0df7ea
8.0.0-20251212052346-61651b0df7ea
go github.com/mattermost/mattermost-server
>=11.1.0
>=10.11.0
>=11.2.0
<5.3.2-0.20251212052346-61651b0df7ea
all versions
>=10.11.0+incompatible
>=11.1.0+incompatible
>=11.2.0+incompatible
5.3.2-0.20251212052346-61651b0df7ea
go github.com/mattermost/mattermost-server/v5
all versions
 no fix listed
go github.com/mattermost/mattermost-server/v6
all versions
 no fix listed

Affected products

  • Mattermost Mattermost

Classification

Weakness
  • CWE-303 Incorrect Implementation of Authentication Algorithm

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.