CVE-2026-5163— Missing authorization check in AI message rewrite endpoint allows access to private thread content
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版本存在安全漏洞，该漏洞源于处理AI辅助消息重写时未验证频道成员身份，可能导致认证攻击者通过特制请求读取私有频道和直接消息中的线程内容。
Possible ATT&CK Techniques 1 AI
T1530 · Data from Cloud StorageAffected Version Matrix 3
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Mattermost | Mattermost | 11.5.0≤ 11.5.1 |
affected |
11.6.0 |
unaffected | ||
11.5.2 |
unaffected |
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I. Basic Information for CVE-2026-5163
Vulnerability Information
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Vulnerability Title
Missing authorization check in AI message rewrite endpoint allows access to private thread content
Source: CVE Program / CVE List V5
Vulnerability Description
Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制缺失
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版本存在安全漏洞，该漏洞源于处理AI辅助消息重写时未验证频道成员身份，可能导致认证攻击者通过特制请求读取私有频道和直接消息中的线程内容。
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-2026-5163
| # | POC Description | Source Link | Shenlong Link |
|---|
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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-2026-6345 | 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 |
| CVE-2026-6334 | 3.1 LOW | OAuth authorization code client binding not enforced during token redemption in Mattermost |
IV. Related Vulnerabilities
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CVE-2026-96260
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CVE-2026-12284
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CVE-2026-75588
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Same vendor: Mattermost
-
CVE-2026-96260
Mattermost server missing request body size limit on plugin -
CVE-2026-96259
Mattermost server-side request forgery via OAuth endpoints c -
CVE-2026-95666
Unbounded post ID array in the bulk reactions endpoint allow -
CVE-2026-12284
Mattermost Desktop App Missing IPC Sender Validation in Call -
CVE-2026-75588
Mattermost Desktop App plugin popout scheme validation bypas
Same weakness: CWE-862
-
CVE-2026-11601
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CVE-2026-97337
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V. Comments for CVE-2026-5163
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