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CVE-2026-3471— Opening a window with {{javascript:alert()}} as URL causes crash in the Mattermost Desktop App

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 Desktop App是美国Mattermost公司的一款消息传递桌面版应用程序。 Mattermost Desktop App 6.1版本、6.0.1版本和5.4.13.0版本存在安全漏洞，该漏洞源于未能阻止无效URL在弹出窗口中加载，可能导致恶意服务器所有者通过调用window.open重复崩溃应用程序。

CVSS 6.5 · Medium EPSS 0.18% · P8

Possible ATT&CK Techniques 1 AI

T1189 · Drive-by Compromise

Affected Version Matrix 5

VendorProduct Version RangeStatus
Mattermost Mattermost ≤ 6.0.1 affected
≤ 5.4.13 affected
6.2.0 unaffected
6.1.1.0 unaffected
5.13.5.0 unaffected
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I. Basic Information for CVE-2026-3471

Vulnerability Information
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Vulnerability Title
Opening a window with {{javascript:alert()}} as URL causes crash in the Mattermost Desktop App
Source: CVE Program / CVE List V5
Vulnerability Description
Mattermost Desktop App versions <=6.1 6.0.1 5.4.13.0 fail to prevent an invalid URL from loading in a pop-up window in the Mattermost Desktop App which allows a malicious server owner to repeated crash the application via calling {{window.open('javascript:alert()');}}. Mattermost Advisory ID: MMSA-2026-00618
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
自定义URL方案处理程序中的授权不正确
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost Desktop App 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost Desktop App是美国Mattermost公司的一款消息传递桌面版应用程序。 Mattermost Desktop App 6.1版本、6.0.1版本和5.4.13.0版本存在安全漏洞，该漏洞源于未能阻止无效URL在弹出窗口中加载，可能导致恶意服务器所有者通过调用window.open重复崩溃应用程序。
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 ~ 6.0.1 -

II. Public POCs for CVE-2026-3471

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III. Intelligence Information for CVE-2026-3471

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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-2026-3637 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-2026-6339 4.3 MEDIUM Missing request origin validation on burn-on-read reveal endpoint
CVE-2026-2325 4.3 MEDIUM Improper Input Validation in MS Teams Meetings API Handler
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-2026-28759 4.3 MEDIUM Insufficient authorization in shared channel membership sync allows remote cluster to remo
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-2026-4286 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

Same product: Mattermost
Same vendor: Mattermost
Same weakness: CWE-939

V. Comments for CVE-2026-3471

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