CVE-2026-5755Network attack vector

Server crash via unvalidated TIFF IFD offset

Published May 22, 2026 · Updated May 22, 2026

Uncontrolled resource consumption in Mattermost allows remote authenticated users to crash the server via crafted TIFF image input. The image-processing path trusts the TIFF Image File Directory offset from the header and allocates memory from that value without validating its bounds. Exploitation requires file-upload or posting permission and either a crafted upload or a posted URL serving one; memory exhaustion causes a server out-of-memory crash.

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

Uncontrolled resource consumption in Mattermost allows remote authenticated users to crash the server via crafted TIFF image input. The image-processing path trusts the TIFF Image File Directory offset from the header and allocates memory from that value without validating its bounds. Exploitation requires file-upload or posting permission and either a crafted upload or a posted URL serving one; memory exhaustion causes a server out-of-memory crash.

The record

CVE
CVE-2026-5755
Published
May 22, 2026
Updated
May 22, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-400, T1499.003
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 22, 2026CVE publishedPublication date reported by the CVE source.
  2. May 22, 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 <=10.11.14
  2. Affected versionversion=11.4.0 <=11.4.4
  3. Affected versionversion=11.5.0 <=11.5.2
  4. Affected versionversion=11.5.0 <=11.5.3
  5. Affected versionversion=11.6.0 <=11.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=10.11.0 <=10.11.14; version=11.4.0 <=11.4.4; version=11.5.0 <=11.5.2; version=11.5.0 <=11.5.3; version=11.6.0 <=11.6.0

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-400Uncontrolled Resource Consumption
T1499.003Application Exhaustion Flood

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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