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Fencer Intel
medium 4.3

CVE-2026-4265 json

Guest user can upload files without permission across teams

published 7mo ago modified 4mo ago also GHSA-xpvf-6qcc-9jqc , GO-2026-4749 , EUVD-2026-12425

cvss
4.3
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 14%
public exploits
0
none known

Summary

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to validate team-specific upload_file permissions which allows a guest user to post files in channels where they lack upload_file permission via uploading files in a team where they have permission and reusing the file metadata in a POST request to a different team. Mattermost Advisory ID: MMSA-2025-00553

Patch / fix

  • go github.com/mattermost/mattermost/server/v8 8.0.0-20260107144005-c7f6efdfb035
  • go github.com/mattermost/mattermost-server 5.3.2-0.20260107144005-c7f6efdfb035, 10.11.11, 10.11.11+incompatible, 11.2.3, 11.2.3+incompatible, 11.3.1, 11.3.1+incompatible
  • Mattermost Mattermost 10.11.11, 11.2.3, 11.3.1, 11.4.0
  • govulncheck-vulndb openSUSE Leap 15.6 0.0.20260326T203309-150000.1.155.2

suse advisories SUSE-SU-2026:1135-1

  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

Is CVE-2026-4265 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7mo ago

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 14% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

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

Affected packages

ecosystem package affected fixed in
go github.com/mattermost/mattermost/server/v8
<8.0.0-20260107144005-c7f6efdfb035
8.0.0-20260107144005-c7f6efdfb035
go github.com/mattermost/mattermost-server
<5.3.2-0.20260107144005-c7f6efdfb035
>=10.11.0-rc1, <10.11.11
>=11.2.0-rc1, <11.2.3
>=11.3.0-rc1, <11.3.1
>=10.11.0-rc1+incompatible, <10.11.11+incompatible
>=11.2.0-rc1+incompatible, <11.2.3+incompatible
>=11.3.0-rc1+incompatible, <11.3.1+incompatible
5.3.2-0.20260107144005-c7f6efdfb035
10.11.11
11.2.3
11.3.1
10.11.11+incompatible
11.2.3+incompatible
11.3.1+incompatible
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

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.