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Description

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

PUBLISHED Reserved 2026-03-16 | Published 2026-03-16 | Updated 2026-03-16 | Assigner Mattermost




MEDIUM: 4.3CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

Problem types

CWE-863: Incorrect Authorization

Product status

Default status
unaffected

11.3.0 (semver)
affected

11.2.0 (semver)
affected

10.11.0 (semver)
affected

11.4.0
unaffected

11.3.1
unaffected

11.2.3
unaffected

10.11.11
unaffected

Credits

0x7oda7123 finder

References

mattermost.com/security-updates (MMSA-2025-00553) vendor-advisory

cve.org (CVE-2026-4265)

nvd.nist.gov (CVE-2026-4265)

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