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

CVSS 6.5 · Medium EPSS 0.03% · P10

Possible ATT&CK Techniques 1AI

T1189 · Drive-by Compromise

Affected Version Matrix 5

VendorProductVersion RangeStatus
MattermostMattermost≤ 6.0.1affected
≤ 5.4.13affected
6.2.0unaffected
6.1.1.0unaffected
5.13.5.0unaffected
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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: NVD (National Vulnerability Database)
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: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Source: NVD (National Vulnerability Database)
Vulnerability Type
自定义URL方案处理程序中的授权不正确
Source: NVD (National Vulnerability Database)

Affected Products

VendorProductAffected VersionsCPESubscribe
MattermostMattermost 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-2026-63468.7 HIGHSensitive credentials exposed in plaintext in Mattermost support packets
CVE-2026-63477.6 HIGHMattermost Calls plugin exposes TURN server credentials in plaintext in support packets
CVE-2026-63456.5 MEDIUMPrevent password disclosure and force reset during Slack import
CVE-2026-51636.5 MEDIUMMissing authorization check in AI message rewrite endpoint allows access to private thread
CVE-2026-31176.5 MEDIUMInstance and webhook GitLab plugin commands were able to be run by non-admin users
CVE-2026-36374.3 MEDIUMMattermost fails to enforce create_post permission when editing posts
CVE-2026-63424.3 MEDIUMGroup prefix matching bypass for subscriptions
CVE-2026-63414.3 MEDIUMIncomplete group locking implementation
CVE-2026-63404.3 MEDIUMMemory Exhaustion via Malicious 7zip File Upload
CVE-2026-63394.3 MEDIUMMissing request origin validation on burn-on-read reveal endpoint
CVE-2026-23254.3 MEDIUMImproper Input Validation in MS Teams Meetings API Handler
CVE-2026-63434.3 MEDIUMMattermost Playbooks Plugin fails to enforce view permissions in list endpoints, allowing
CVE-2026-287324.3 MEDIUMSlash command trigger-word update allowed command hijacking
CVE-2026-287594.3 MEDIUMInsufficient authorization in shared channel membership sync allows remote cluster to remo
CVE-2026-34953.8 LOWUnescaped variables during error page composition
CVE-2026-42733.7 LOWInsufficient token rotation validation in remote cluster invite confirmation
CVE-2026-63333.5 LOWSSRF via Host Header Spoofing in Custom Slash Commands
CVE-2026-46433.5 LOWCalling window.close() from server-side content causes crash in the Mattermost Desktop App
CVE-2026-42863.1 LOWPlaybooks Plugin fails to validate team transfers, allowing unauthorized removal of member
CVE-2026-63343.1 LOWOAuth 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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