CVE-2025-21088Network attack vector

Frontend crash via unvalidated attachment proto style

Published Jan 15, 2025 · Updated Jan 15, 2025

Incorrect type conversion in Mattermost 10.2.0 allows remote authenticated users to crash the web frontend via a crafted post attachment. The attachment handler fails to validate the type of the proto style supplied to an action's style in post.props.attachments before frontend processing. Low-privileged account access is sufficient; affected releases are 9.11.0 through 9.11.5, 10.0.0 through 10.0.3, 10.1.0 through 10.1.3, and 10.2.0.

CVSS severity6.5
Medium
EPSS probability0.56%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect type conversion in Mattermost 10.2.0 allows remote authenticated users to crash the web frontend via a crafted post attachment. The attachment handler fails to validate the type of the proto style supplied to an action's style in post.props.attachments before frontend processing. Low-privileged account access is sufficient; affected releases are 9.11.0 through 9.11.5, 10.0.0 through 10.0.3, 10.1.0 through 10.1.3, and 10.2.0.

The record

CVE
CVE-2025-21088
Published
Jan 15, 2025
Updated
Jan 15, 2025
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-704, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 15, 2025CVE publishedPublication date reported by the CVE source.
  2. Jan 15, 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=10.0.0 <=10.0.3
  2. Affected versionversion=10.1.0 <=10.1.3
  3. Affected versionversion=10.2.0
  4. Affected versionversion=9.11.0 <=9.11.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=10.0.0 <=10.0.3; version=10.1.0 <=10.1.3; version=10.2.0; version=9.11.0 <=9.11.5

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.

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

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-704Incorrect Type Conversion or Cast
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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