CVE-2025-12689Network attack vector

Authenticated Calls crash via invalid UTF-8 action

Published Dec 17, 2025 · Updated Dec 17, 2025

Input validation in Mattermost 10.11.0 through 10.11.6 allows remote authenticated users to crash the bundled Calls plugin. WebSocketMessageHasBeenPosted processes req.Action without first rejecting invalid UTF-8, allowing malformed action bytes to reach the handler. The Calls plugin must be enabled; 10.12.0 through 10.12.2 and 11.0.0 through 11.0.4 are also affected, with no reported data exposure or modification.

CVSS severity6.5
Medium
EPSS probability0.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Input validation in Mattermost 10.11.0 through 10.11.6 allows remote authenticated users to crash the bundled Calls plugin. WebSocketMessageHasBeenPosted processes req.Action without first rejecting invalid UTF-8, allowing malformed action bytes to reach the handler. The Calls plugin must be enabled; 10.12.0 through 10.12.2 and 11.0.0 through 11.0.4 are also affected, with no reported data exposure or modification.

The record

CVE
CVE-2025-12689
Published
Dec 17, 2025
Updated
Dec 17, 2025
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-1287, T1499
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 17, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 17, 2025Record 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=10.11.0 <=10.11.6
  2. Affected versionversion=10.12.0 <=10.12.2
  3. Affected versionversion=11.0.0 <=11.0.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=10.11.0 <=10.11.6; version=10.12.0 <=10.12.2; version=11.0.0 <=11.0.4

Published CVSS scores

6.5Mattermost, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1287Improper Validation of Specified Type of Input
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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