Vulnerability · Published Oct 16, 2026 · Assigned by Mattermost

CVE-2026-16251Mattermost local image proxy allows server memory exhaustion via unbounded image response buffering

Medium 6.5

In plain English

A medium-severity resource allocation without limits 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 0.3% (higher than 21% of all known vulnerabilities).

Severity (CVSS 3.1)6.5Medium

Exploit odds (30 days)0.3%top 78.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to limit the size of remote image responses buffered in memory during local image proxy direct fetches, which allows a remote attacker to cause memory exhaustion on the server via a crafted oversized image response.. Mattermost Advisory ID: MMSA-2026-00726

Affected products (as reported)

Vendor	Product	Versions
Mattermost	Mattermost	11.10.0 – through 11.10.011.7.0 – through 11.7.911.9.0 – through 11.9.111.8.0 – through 11.8.5

Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

References

MMSA-2026-00726 vendor-advisory