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🛡️ CVE-2026-5755 — mattermost-server

🟡 CVSS 6.5 — Medium ✅ No Known Exploit CWE-400 NVD
6.5
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Mattermost doesn't validate the TIFF IFD offset in the image header before allocating memory

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.2, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the TIFF IFD offset in the image header before allocating memory, which allows authenticated users with file upload or posting permissions to cause a denial of service (server OOM) via uploading a crafted TIFF file or posting a URL that serves one.. Mattermost Advisory ID: MMSA-2026-00648

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: Low — an ordinary user account is enough.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-5755 is classified as CWE-400: Uncontrolled Resource Consumption. A request can consume memory, CPU or storage without limit, exhausting capacity for everyone else.

Affected software

CVE-2026-5755 is recorded against 2 packages.

  • github.com/mattermost/mattermost-server
  • mattermost-server (from 11.6.0 up to 11.6.1)

Timeline and source

Published on 7 July 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com (Advisory)
nvd.nist.gov (Advisory)
github.com (Web)
mattermost.com (Web)

Other advisories for this package

github.com/mattermost/mattermost-server has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-400: Uncontrolled Resource Consumption) in other software:

Details

Severity Medium
CVSS Score 6.5
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CWE CWE-400
Public Exploit ✅ No
Source NVD
Published 2026-07-07
Updated 2026-08-20
Modified 2026-07-07
Fix URL N/A

Affected Packages

Software From version Fixed in
github.com/mattermost/mattermost-server — —
mattermost-server 11.6.0 11.6.1

Similar Threats

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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