libwebsockets MQTT Protocol PUBACK Packet Handling Out-Of-Bounds Write Remote Code Execution Vulnerability

October 26th, 2026
ZDI-26-792 ZDI-CAN-31039

CVE ID

CVE-2026-114550

CVSS Score

8.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors

libwebsockets

Affected Products

libwebsockets

Vulnerability Details

This vulnerability allows remote attackers to execute arbitrary code on affected installations of libwebsockets. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the handling of PUBACK packets. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process.

Additional Details

libwebsockets has issued an update to correct this vulnerability. More details can be found at:
https://github.com/warmcat/libwebsockets/commit/c9e8e1834d7f13038c82963086b90e2ee9c5b44c

Disclosure Timeline

  • 2026-07-16 - Vulnerability reported to vendor
  • 2026-10-26 - Coordinated public release of advisory
  • 2026-10-26 - Advisory Updated

Credit

Anonymous

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