libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability

August 24th, 2026
ZDI-26-590 ZDI-CAN-31036

CVE ID

CVE-2026-19773

CVSS Score

9.8 AV:N/AC:L/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 parsing of HTTP/2 HPACK path header. 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/824151862f37bc72f46d9a3e01d5b9408d313a0b

Disclosure Timeline

  • 2026-07-03 - Vulnerability reported to vendor
  • 2026-08-24 - Coordinated public release of advisory
  • 2026-08-24 - Advisory Updated

Credit

Maher Azzouzi

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