CVE-2026-28735— GitHub OAuth Scope Validation
Possible ATT&CK Techniques 1AI
T1190 · Exploit Public-Facing ApplicationAffected Version Matrix 9
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Mattermost | Mattermost | 11.6.0≤ 11.6.0 | affected |
11.5.0≤ 11.5.3 | affected | ||
11.4.0≤ 11.4.4 | affected | ||
10.11.0≤ 10.11.14 | affected | ||
11.7.0 | unaffected | ||
11.6.1 | unaffected | ||
11.5.4 | unaffected | ||
11.4.5 | unaffected | ||
| … +1 more rows | |||
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I. Basic Information for CVE-2026-28735
Vulnerability Information
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Vulnerability Title
GitHub OAuth Scope Validation
Source: CVE Program / CVE List V5
Vulnerability 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
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制不正确
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 11.6.0及之前的11.6.x版本、11.5.3及之前的11.5.x版本、11.4.4及之前的11.4.x版本和10.11.14及之前的10.11.x版本存在安全漏洞，该漏洞源于未验证回调中的OAuth令牌范围，可能导致经过身份验证的Mattermost用户通过修改GitHub授权URL中的范围参数访问私有仓库。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| Mattermost | Mattermost | 11.6.0 ~ 11.6.0 | - |
II. Public POCs for CVE-2026-28735
| # | POC Description | Source Link | Shenlong Link |
|---|
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Same Patch Batch · Mattermost · 2026-05-22 · 8 CVEs total
| CVE-2026-5740 | 7.5 HIGH | Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server |
| CVE-2026-4635 | 6.5 MEDIUM | Persistent notification timing attack causing server denial of service |
| CVE-2026-5755 | 6.5 MEDIUM | Denial of service via crafted TIFF file upload |
| CVE-2026-3473 | 5.9 MEDIUM | Improper file ownership validation in the Boards API allows unauthorised file access |
| CVE-2026-5308 | 4.9 MEDIUM | Missing request body size limits on Zoom plugin HTTP endpoints |
| CVE-2026-4646 | 4.3 MEDIUM | Insufficient input validation in GitHub plugin API causes denial of service |
| CVE-2026-3636 | 4.3 MEDIUM | Sanitize team member data returned by API |
IV. Related Vulnerabilities
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Insufficient server-side validation of board member role fie - CVE-2026-10080
Boards plugin panics on WebSocket command with non-string fi
Same vendor: Mattermost
- CVE-2026-75587
Plaintext pre-auth secret exposure via Desktop App diagnosti - CVE-2026-9693
Mattermost thread memberships persist after team removal, ex - CVE-2026-9859
Mattermost Boards plugin didn’t enforce role-based authoriza - CVE-2026-9816
Insufficient server-side validation of board member role fie - CVE-2026-10080
Boards plugin panics on WebSocket command with non-string fi
Same weakness: CWE-863
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