CVE-2026-4265Guest user can upload files without permission across teams
- 4.3MediumCVSS base score
- 0.25%Exploitation in 30 daysEPSS · top 83% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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
Timeline
ID reserved
By Mattermost
Published
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| MattermostCNA (assigner) | 3.1 | Medium4.3 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N |
| NVDNVD · Analyzed | 3.1 | Medium4.3 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N |
- EPSS (exploitation in 30 days)
- 0.25% · top 83% of all CVEs (12 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 4.3.
Affected products
- affected 11.3.0 – ≤ 11.3.0
- affected 11.2.0 – ≤ 11.2.2
- affected 10.11.0 – ≤ 10.11.10
- unaffected 11.4.0
- unaffected 11.3.1
- unaffected 11.2.3
- unaffected 10.11.11
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- Gogithub.com/mattermost/mattermost-serverGHSA-xpvf-6qcc-9jqc (opens in a new tab)
- Gogithub.com/mattermost/mattermost/server/v8GHSA-xpvf-6qcc-9jqc (opens in a new tab)
What to do
Solution: Update Mattermost to versions 11.4.0, 11.3.1, 11.2.3, 10.11.11 or higher.
References
References1
- MMSA-2025-00553 (opens in a new tab)vendor-advisory
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-12425 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-xpvf-6qcc-9jqc (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-4265)Record last updated .