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CVE-2026-6334— OAuth authorization code client binding not enforced during token redemption in Mattermost

Quick assessment

Affected
Mattermost Mattermost
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 11.5.1及之前的11.5.x版本和10.11.13及之前的10.11.x版本存在安全漏洞，该漏洞源于OAuth授权码兑换流程中未强制客户端身份绑定，可能导致认证OAuth客户端通过特制令牌交换请求兑换颁发给不同客户端的授权码。

CVSS 3.1 · Low EPSS 0.12% · P2

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 5

VendorProduct Version RangeStatus
Mattermost Mattermost 11.5.0≤ 11.5.1 affected
10.11.0≤ 10.11.13 affected
11.6.0 unaffected
11.5.2 unaffected
10.11.14 unaffected
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I. Basic Information for CVE-2026-6334

Vulnerability Information
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Vulnerability Title
OAuth authorization code client binding not enforced during token redemption in Mattermost
Source: CVE Program / CVE List V5
Vulnerability Description
Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to enforce client identity binding during the OAuth authorization code redemption flow which allows an authenticated OAuth client to redeem authorization codes issued to a different client via a crafted token exchange request.. Mattermost Advisory ID: MMSA-2026-00570
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用基本弱点进行的认证绕过
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 11.5.1及之前的11.5.x版本和10.11.13及之前的10.11.x版本存在安全漏洞，该漏洞源于OAuth授权码兑换流程中未强制客户端身份绑定，可能导致认证OAuth客户端通过特制令牌交换请求兑换颁发给不同客户端的授权码。
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 11.5.0 ~ 11.5.1 -

II. Public POCs for CVE-2026-6334

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III. Intelligence Information for CVE-2026-6334

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Same Patch Batch · Mattermost · 2026-05-18 · 21 CVEs total

CVE-2026-6346 8.7 HIGH Sensitive credentials exposed in plaintext in Mattermost support packets
CVE-2026-6347 7.6 HIGH Mattermost Calls plugin exposes TURN server credentials in plaintext in support packets
CVE-2026-3471 6.5 MEDIUM Opening a window with {{javascript:alert()}} as URL causes crash in the Mattermost Desktop
CVE-2026-3117 6.5 MEDIUM Instance and webhook GitLab plugin commands were able to be run by non-admin users
CVE-2026-5163 6.5 MEDIUM Missing authorization check in AI message rewrite endpoint allows access to private thread
CVE-2026-6345 6.5 MEDIUM Prevent password disclosure and force reset during Slack import
CVE-2026-28732 4.3 MEDIUM Slash command trigger-word update allowed command hijacking
CVE-2026-6343 4.3 MEDIUM Mattermost Playbooks Plugin fails to enforce view permissions in list endpoints, allowing
CVE-2026-28759 4.3 MEDIUM Insufficient authorization in shared channel membership sync allows remote cluster to remo
CVE-2026-2325 4.3 MEDIUM Improper Input Validation in MS Teams Meetings API Handler
CVE-2026-6339 4.3 MEDIUM Missing request origin validation on burn-on-read reveal endpoint
CVE-2026-6340 4.3 MEDIUM Memory Exhaustion via Malicious 7zip File Upload
CVE-2026-6341 4.3 MEDIUM Incomplete group locking implementation
CVE-2026-6342 4.3 MEDIUM Group prefix matching bypass for subscriptions
CVE-2026-3637 4.3 MEDIUM Mattermost fails to enforce create_post permission when editing posts
CVE-2026-3495 3.8 LOW Unescaped variables during error page composition
CVE-2026-4273 3.7 LOW Insufficient token rotation validation in remote cluster invite confirmation
CVE-2026-4643 3.5 LOW Calling window.close() from server-side content causes crash in the Mattermost Desktop App
CVE-2026-6333 3.5 LOW SSRF via Host Header Spoofing in Custom Slash Commands
CVE-2026-4286 3.1 LOW Playbooks Plugin fails to validate team transfers, allowing unauthorized removal of member

IV. Related Vulnerabilities

Same product: Mattermost
Same vendor: Mattermost
Same weakness: CWE-305

V. Comments for CVE-2026-6334

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