CVE-2026-3471Network attack vector

Client crash via unblocked javascript pop-up URL

Published May 18, 2026 · Updated May 18, 2026

Improper URL authorization in Mattermost Desktop App 5.4.13 and earlier, 6.0.1 and earlier, and 6.1.0 allows remote attackers to crash the client. A server-controlled renderer can call window.open with a javascript: URL, and the client loads that invalid URL in a pop-up instead of rejecting it. The attacker must control a server to which the user connects and induce user interaction; repeated calls repeatedly terminate the desktop application without affecting confidentiality or integrity.

CVSS severity6.5
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper URL authorization in Mattermost Desktop App 5.4.13 and earlier, 6.0.1 and earlier, and 6.1.0 allows remote attackers to crash the client. A server-controlled renderer can call window.open with a javascript: URL, and the client loads that invalid URL in a pop-up instead of rejecting it. The attacker must control a server to which the user connects and induce user interaction; repeated calls repeatedly terminate the desktop application without affecting confidentiality or integrity.

The record

CVE
CVE-2026-3471
Published
May 18, 2026
Updated
May 18, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-939, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 18, 2026CVE publishedPublication date reported by the CVE source.
  2. May 18, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=5.4.13
  2. Affected versionversion=0 <=6.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mattermost · Mattermostversion=0 <=5.4.13; version=0 <=6.0.1

Published CVSS scores

6.5Mattermost, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-939Improper Authorization in Handler for Custom URL Scheme
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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