PT-2026-42750 · Mattermost · Mattermost

Zephrfish · Published 2026-05-22 · Updated 2026-07-07 · CVE-2026-5740

Positive Technologies (AI Summary)

CVSS v2.0

7.8

High

Base vector

AV:N/AC:L/Au:N/C:N/I:N/A:C

Name of the Vulnerable Software and Affected Versions Mattermost version 11.6.0 Mattermost version 11.5.3 Mattermost version 11.4.4 Mattermost version 10.11.14

Description An issue exists where msgpack-encoded WebSocket frames are not properly validated before memory allocation. This allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users by sending a crafted binary WebSocket message to the public WebSocket endpoint.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.

Exploit

DoS

Weakness Enumeration

CWE-789

Related Identifiers

BDU:2026-07533

CVE-2026-5740

GHSA-W9M8-P4CC-4QJ9

GO-2026-5838

Affected Products

Mattermost

References · 13

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/5xxx/CVE-2026-5740.json · Exploit
• https://osv.dev/vulnerability/CVE-2026-5740 · Vendor Advisory
• https://bdu.fstec.ru/vul/2026-07533 · Security Note
• https://mattermost.com/security-updates · Vendor Advisory
• https://osv.dev/vulnerability/GHSA-w9m8-p4cc-4qj9 · Vendor Advisory
• https://osv.dev/vulnerability/GO-2026-5838 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-5740 · Security Note
• https://github.com/mattermost/mattermost/commit/17939826efa20a97f087b3d390ec5136df350bae · Note
• https://github.com/mattermost/mattermost · Note
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-5740 · Note
• https://github.com/advisories/GHSA-w9m8-p4cc-4qj9 · Note
• https://vuldb.com/vuln/365177 · Note
• https://t.me/CVEtracker/54622 · Telegram Post