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Critical · 9.8 CVE-2026-19773 EUVD-2026-79130GHSA-r4m8-276f-3r2f

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

Published Sep 15, 2026 · Updated Sep 16, 2026 · Assigned by zdi

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 products

VendorProductAffectedFixed
libwebsockets libwebsockets b4b5aed3903eaff09cd76a410f69bbe5dff66f8e —

Fixed in Linux distributions

Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.

ReleasePackageFixed inAdvisory
Debian 14 libwebsockets 4.3.5-7 —
Debian 13 libwebsockets 4.3.5-1+deb13u3 —
Debian 12 libwebsockets No fix yet —
ReleasePackageFixed inAdvisory
Ubuntu Pro 26.04 LTS libwebsockets 4.3.5-3ubuntu1.2+esm1 USN-8893-1
Ubuntu Pro 24.04 LTS libwebsockets 4.3.3-1.1ubuntu0.1~esm3 USN-8893-1
Ubuntu Pro 22.04 LTS libwebsockets 4.0.20-2ubuntu1.1+esm2 USN-8893-1
Show 3 more (older releases, extended support, other products)
ReleasePackageFixed inAdvisory
Ubuntu Pro 20.04 LTS libwebsockets 3.2.1-3ubuntu0.1~esm3 USN-8893-1
Ubuntu Pro 18.04 LTS libwebsockets 2.0.3-3ubuntu0.1~esm1 USN-8893-1
Ubuntu Pro 16.04 LTS libwebsockets 1.7.1-1ubuntu0.1~esm1 USN-8893-1

Advisories 1

References