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CVE-2026-9699— Mattermost Agents plugin logs unsanitized OpenAI API keys on authentication errors

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公司开源的一个开源协作平台。 Mattermost 10.18.11及之前版本、11.3.6及之前版本和11.6.5.0及之前版本存在信息泄露漏洞，该漏洞源于日志记录前未对来自OpenAI API的错误响应进行清理，可能导致具有服务器日志或支持数据包访问权限的用户通过检查认证失败期间生成的mattermost.log条目获取有效或可部分重建的OpenAI API密钥。

CVSS 6.8 · Medium EPSS 0.46% · P38

Possible ATT&CK Techniques 1 AI

T1530 · Data from Cloud Storage

Affected Version Matrix 7

VendorProduct Version RangeStatus
Mattermost Mattermost ≤ 10.18.11 affected
≤ 11.3.6 affected
≤ 11.6.5 affected
11.7.0 unaffected
10.11.19 unaffected
11.6.4 unaffected
11.5.7 unaffected
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I. Basic Information for CVE-2026-9699

Vulnerability Information
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Vulnerability Title
Mattermost Agents plugin logs unsanitized OpenAI API keys on authentication errors
Source: CVE Program / CVE List V5
Vulnerability Description
Mattermost Plugins versions <=11.6 10.18.11 11.3.6 11.6.5.0 fail to sanitize error responses from the OpenAI API before logging, which allows a user with access to server logs or support packets to obtain a valid or partially reconstructable OpenAI API key via inspection of mattermost.log entries generated during authentication failures. Mattermost Advisory ID: MMSA-2026-00609
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
通过日志文件的信息暴露
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost 信息泄露漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司开源的一个开源协作平台。 Mattermost 10.18.11及之前版本、11.3.6及之前版本和11.6.5.0及之前版本存在信息泄露漏洞，该漏洞源于日志记录前未对来自OpenAI API的错误响应进行清理，可能导致具有服务器日志或支持数据包访问权限的用户通过检查认证失败期间生成的mattermost.log条目获取有效或可部分重建的OpenAI API密钥。
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 0 ~ 10.18.11 -

II. Public POCs for CVE-2026-9699

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III. Intelligence Information for CVE-2026-9699

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Same Patch Batch · Mattermost · 2026-06-26 · 4 CVEs total

CVE-2026-4339 6.5 MEDIUM SSRF via unvalidated attachment URLs in Mattermost Agents plugin MCP server
CVE-2026-13426 5.4 MEDIUM Client4 fails to validate path parameters
CVE-2026-3472 3.5 LOW Markdown image rendering bypass in AI bot tool result posts in Mattermost

IV. Related Vulnerabilities

Same product: Mattermost
Same vendor: Mattermost
Same weakness: CWE-532

V. Comments for CVE-2026-9699

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