CVE-2026-10819Network attack vector

Authenticated service interruption via unbounded GIF frames

Published Jul 27, 2026 · Updated Jul 27, 2026

Denial of service in Mattermost Server allows remote authenticated users to interrupt service via a crafted animated GIF custom emoji. The custom-emoji upload path processes animated GIFs without limiting frame count or enforcing the file-size cap, allowing resource use to grow with crafted content. Any authenticated user permitted to upload custom emoji can cause a service-wide availability loss; the published record reports no data disclosure or modification.

CVSS severity6.5
Medium
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Mattermost Server allows remote authenticated users to interrupt service via a crafted animated GIF custom emoji. The custom-emoji upload path processes animated GIFs without limiting frame count or enforcing the file-size cap, allowing resource use to grow with crafted content. Any authenticated user permitted to upload custom emoji can cause a service-wide availability loss; the published record reports no data disclosure or modification.

The record

CVE
CVE-2026-10819
Published
Jul 27, 2026
Updated
Jul 27, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-409, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 27, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 27, 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=10.11.0 <=10.11.20
  2. Affected versionversion=11.6.0 <=11.6.5
  3. Affected versionversion=11.7.0 <=11.7.4
  4. Affected versionversion=11.8.0 <=11.8.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=10.11.0 <=10.11.20; version=11.6.0 <=11.6.5; version=11.7.0 <=11.7.4; version=11.8.0 <=11.8.1

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-409Improper Handling of Highly Compressed Data (Data Amplification)
T1499.004Endpoint Denial of Service: Application 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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