CVE-2026-8683Network attack vector

Client crash via unbounded window.open URL

Published Jun 15, 2026 · Updated Jun 15, 2026

Resource exhaustion in Mattermost Desktop App through 5.5.13 allows remote attackers controlling a server to crash the client. A server-supplied script calls window.open with an extremely long URL, and the desktop client processes it without enforcing a length or resource limit. The target must connect the desktop app to the malicious server and interact with its content; the demonstrated consequence is an application crash.

CVSS severity6.5
Medium
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Mattermost Desktop App through 5.5.13 allows remote attackers controlling a server to crash the client. A server-supplied script calls window.open with an extremely long URL, and the desktop client processes it without enforcing a length or resource limit. The target must connect the desktop app to the malicious server and interact with its content; the demonstrated consequence is an application crash.

The record

CVE
CVE-2026-8683
Published
Jun 15, 2026
Updated
Jun 15, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-770, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 15, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 15, 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 <=5.5.13

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mattermost · Mattermostversion=0 <=5.5.13

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
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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