Vulnerability · Published Sep 15, 2026 · Assigned by zdi

CVE-2026-19773libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability

Critical 9.8

In plain English

A critical-severity out-of-bounds write in libwebsockets from libwebsockets. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 51% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.0)9.8Critical

Exploit odds (30 days)0.6%top 48.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

libwebsockets HTTP/2 HPACK Path Header Parsing Out-Of-Bounds Write Remote Code Execution Vulnerability. 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. Was ZDI-CAN-31036.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	libwebsockets	no fix listed	DEBIAN-CVE-2026-19773
Debian:13	libwebsockets	4.3.5-1+deb13u3	DEBIAN-CVE-2026-19773
Debian:14	libwebsockets	4.3.5-7	DEBIAN-CVE-2026-19773

Affected products (as reported)

Vendor	Product	Versions
libwebsockets	libwebsockets	b4b5aed3903eaff09cd76a410f69bbe5dff66f8e

Weakness: CWE-787 · Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References

ZDI-26-590 x_research-advisory
vendor-provided URL vendor-advisory