CVE-2026-16251 PUBLISHED

Mattermost local image proxy allows server memory exhaustion via unbounded image response buffering

Assigner: Mattermost
Reserved: 20.07.2026 Published: 16.10.2026 Updated: 16.10.2026

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

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CVSS Score: 6.5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	Low	Integrity Impact	None
User Interaction	None	Availability Impact	High

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.10.0 to 11.10.0 (incl.) affected from 11.7.0 to 11.7.9 (incl.) affected from 11.9.0 to 11.9.1 (incl.) affected from 11.8.0 to 11.8.5 (incl.) Version 11.11.0 is unaffected Version 11.10.1 is unaffected Version 11.7.10 is unaffected Version 11.9.2 is unaffected Version 11.8.6 is unaffected

Solutions

Update Mattermost to versions 11.11.0, 11.10.1, 11.7.10, 11.9.2, 11.8.6 or higher.

Credits

alimursaliyev finder

References

MMSA-2026-00726

Problem Types

CWE-770: Allocation of Resources Without Limits or Throttling CWE