CVE-2026-6339— Missing request origin validation on burn-on-read reveal endpoint
Possible ATT&CK Techniques 1AI
T1190 · Exploit Public-Facing ApplicationAffected Version Matrix 5
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Mattermost | Mattermost | 11.5.0≤ 11.5.1 | affected |
11.4.0≤ 11.4.3 | affected | ||
11.6.0 | unaffected | ||
11.5.2 | unaffected | ||
11.4.4 | unaffected |
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I. Basic Information for CVE-2026-6339
Vulnerability Information
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Vulnerability Title
Missing request origin validation on burn-on-read reveal endpoint
Source: NVD (National Vulnerability Database)
Vulnerability Description
Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636
Source: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Source: NVD (National Vulnerability Database)
Vulnerability Type
源验证错误
Source: NVD (National Vulnerability Database)
Vulnerability Title
Mattermost 访问控制错误漏洞
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11.4.3及之前的11.4.x版本存在访问控制错误漏洞，该漏洞源于未能验证burn-on-read揭示端点的X-Requested-With标头，可能导致经过身份验证的频道成员通过特制的Markdown图片标签强制揭示burn-on-read消息而无需收件人同意。
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-2026-6339
| # | 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-2026-6345 | 6.5 MEDIUM | Prevent password disclosure and force reset during Slack import |
| CVE-2026-5163 | 6.5 MEDIUM | Missing authorization check in AI message rewrite endpoint allows access to private thread |
| CVE-2026-3117 | 6.5 MEDIUM | Instance and webhook GitLab plugin commands were able to be run by non-admin users |
| CVE-2026-3471 | 6.5 MEDIUM | Opening a window with {{javascript:alert()}} as URL causes crash in the Mattermost Desktop |
| 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-2026-3637 | 4.3 MEDIUM | Mattermost fails to enforce create_post permission when editing posts |
| CVE-2026-6342 | 4.3 MEDIUM | Group prefix matching bypass for subscriptions |
| CVE-2026-6341 | 4.3 MEDIUM | Incomplete group locking implementation |
| CVE-2026-6340 | 4.3 MEDIUM | Memory Exhaustion via Malicious 7zip File Upload |
| CVE-2026-6343 | 4.3 MEDIUM | Mattermost Playbooks Plugin fails to enforce view permissions in list endpoints, allowing |
| CVE-2026-28732 | 4.3 MEDIUM | Slash command trigger-word update allowed command hijacking |
| 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-2026-6333 | 3.5 LOW | SSRF via Host Header Spoofing in Custom Slash Commands |
| CVE-2026-4643 | 3.5 LOW | Calling window.close() from server-side content causes crash in the Mattermost Desktop App |
| CVE-2026-6334 | 3.1 LOW | OAuth authorization code client binding not enforced during token redemption in Mattermost |
| CVE-2026-4286 | 3.1 LOW | Playbooks Plugin fails to validate team transfers, allowing unauthorized removal of member |
IV. Related Vulnerabilities
Same product: Mattermost
- CVE-2026-3471
Opening a window with {{javascript:alert()}} as URL causes c - CVE-2026-4643
Calling window.close() from server-side content causes crash - CVE-2026-6333
SSRF via Host Header Spoofing in Custom Slash Commands - CVE-2026-6345
Prevent password disclosure and force reset during Slack imp - CVE-2026-6346
Sensitive credentials exposed in plaintext in Mattermost sup
Same vendor: Mattermost
- CVE-2026-3471
Opening a window with {{javascript:alert()}} as URL causes c - CVE-2026-4643
Calling window.close() from server-side content causes crash - CVE-2026-6333
SSRF via Host Header Spoofing in Custom Slash Commands - CVE-2026-6345
Prevent password disclosure and force reset during Slack imp - CVE-2026-6346
Sensitive credentials exposed in plaintext in Mattermost sup
Same weakness: CWE-346
- CVE-2026-2611
Improper Origin Validation in mlflow/mlflow - CVE-2026-46728
DENX Software Engineering Das U-Boot 访问控制错误漏洞 - CVE-2026-42559
RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP se - CVE-2026-44184
Cleanuparr: Reflective CORS combined with trusted-network au - CVE-2026-6508
RCE in TUBITAK BILGEM's Liderahenk
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