PT-2026-42799 · Mattermost · Mattermost

Eahmed · CVE-2026-28735 · Published 2026-05-22 · Updated 2026-07-07

Positive Technologies (AI Summary)

CVSS v3.1

5.4

Medium

Base vector

AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

Name of the Vulnerable Software and Affected Versions Mattermost version 11.6.0 Mattermost version 11.5.3 Mattermost version 11.4.4 Mattermost version 10.11.14

Description An issue exists where the software fails to validate the OAuth token scope during the callback process. This allows an authenticated user to gain unauthorized access to private repositories by modifying the scope parameter within the GitHub authorization URL.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.

Exploit

DoS

Incorrect Authorization

Weakness Enumeration

CWE-863

Related Identifiers

CVE-2026-28735

GHSA-R5VF-GRCX-5VQP

GO-2026-5839

Affected Products

Mattermost

References · 11

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/28xxx/CVE-2026-28735.json · Exploit
• https://mattermost.com/security-updates · Vendor Advisory
• https://osv.dev/vulnerability/CVE-2026-28735 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-28735 · Security Note
• https://osv.dev/vulnerability/GHSA-r5vf-grcx-5vqp · Vendor Advisory
• https://osv.dev/vulnerability/GO-2026-5839 · Vendor Advisory
• https://github.com/mattermost/mattermost · Note
• https://github.com/mattermost/mattermost-plugin-github/commit/6e6b740c4852cdfa136ee0ced160da832285c353 · Note
• https://t.me/CVEtracker/54650 · Telegram Post
• https://github.com/advisories/GHSA-r5vf-grcx-5vqp · Note
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-28735 · Note