# CVE-2026-28735: GitHub OAuth Scope Validation

> CVE-2026-28735: GitHub OAuth Scope Validation. CVSS 5.4 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-28735
Last updated: 2026-07-23T16:10:00Z

- Published: 2026-05-22 16:26 UTC · Updated: 2026-07-23 16:10 UTC · Assigner: Mattermost
- CVSS: 5.4 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
- EPSS: 0.14%, 3th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-863

## Description

Mattermost versions 11.6.x \<= 11.6.0, 11.5.x \<= 11.5.3, 11.4.x \<= 11.4.4, 10.11.x \<= 10.11.14 fail to validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL.. Mattermost Advisory ID: MMSA-2026-00628

## Affected vendors and products

- Mattermost: Mattermost

## Tracked companies

- [Mattermost](https://rewindex.com/company/mattermost.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-28735)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-28735)
- [https://mattermost.com/security-updates](https://mattermost.com/security-updates)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-28735 · Markdown: https://rewindex.com/cve/CVE-2026-28735.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-28735 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T04:04:11.015Z