Vulnerability · Published Sep 14, 2026 · Assigned by Mattermost

CVE-2026-15814Uploading a crafted image causes excessive memory allocation in the Mattermost Server

Medium 6.5

In plain English

A medium-severity security flaw in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 37% of all known vulnerabilities).

Severity (CVSS 3.1)6.5Medium

Exploit odds (30 days)0.4%top 63.5% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to limit the amount of memory allocated when decoding uploaded image files which allows an authenticated user to cause excessive server memory consumption and potential denial of service via uploading a specially crafted image as a profile picture, channel file attachment, team icon, or custom brand image. Mattermost Advisory ID: MMSA-2026-00719

Affected products (as reported)

Vendor	Product	Versions
Mattermost	Mattermost	11.9.0 – through 11.9.011.8.0 – through 11.8.411.7.0 – through 11.7.710.11.0 – through 10.11.22

Weakness: CWE-409 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

References

MMSA-2026-00719 vendor-advisory