CVE-2026-93849 PUBLISHED

Mattermost allows authenticated users to trigger excessive memory allocation via crafted msgpack binary WebSocket frames

Assigner: Mattermost
Reserved: 18.09.2026 Published: 26.10.2026 Updated: 26.10.2026

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 Mattermost fail to apply allocation limits to the byte-string decode paths in its WebSocket msgpack decoder, which allows an authenticated remote attacker to cause excessive server memory allocation via a crafted binary WebSocket frame declaring a Bin32 payload length of up to 4,294,967,295 bytes.. Mattermost Advisory ID: MMSA-2026-00768

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 11.9.0 to 11.9.1 (incl.) affected from 11.8.0 to 11.8.5 (incl.) affected from 11.7.0 to 11.7.10 (incl.) affected from 11.10.0 to 11.10.1 (incl.) Version 11.11.0 is unaffected Version 11.9.2 is unaffected Version 11.8.6 is unaffected Version 11.7.11 is unaffected Version 11.10.2 is unaffected

Solutions

Update Mattermost to versions 11.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2 or higher.

Credits

oduoke finder

References

MMSA-2026-00768

Problem Types

CWE-789: Memory Allocation with Excessive Size Value CWE