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Fencer Vulns
critical 9.8

CVE-2026-19773 json

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

published 2026-09-15 54 d ago modified 2026-09-18 51 d ago also EUVD-2026-79130

cvss
9.8
version 3.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 51%
public exploits
0
none known

Summary

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.

Patch / fix

  • libwebsockets Debian 13 4.3.5-1+deb13u3
  • libwebsockets Debian 14 4.3.5-7

debian advisories DEBIAN-CVE-2026-19773

  • libwebsockets Ubuntu Pro 16.04 LTS 1.7.1-1ubuntu0.1~esm1
  • libwebsockets Ubuntu Pro 18.04 LTS 2.0.3-3ubuntu0.1~esm1
  • libwebsockets Ubuntu Pro 20.04 LTS 3.2.1-3ubuntu0.1~esm3
  • libwebsockets Ubuntu Pro 22.04 LTS 4.0.20-2ubuntu1.1+esm2
  • libwebsockets Ubuntu Pro 24.04 LTS 4.3.3-1.1ubuntu0.1~esm3
  • libwebsockets Ubuntu Pro 26.04 LTS 4.3.5-3ubuntu1.2+esm1

ubuntu advisories UBUNTU-CVE-2026-19773

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-19773 updated cvss 9.8

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

  • Red Hat A-MQ Interconnect 1 libwebsockets Red Hat Service Interconnect 2 libwebsockets
    affected: workaround, no fix available
  • Red Hat OpenStack Platform 16.2 libwebsockets Red Hat OpenStack Platform 17.1 libwebsockets
    under investigation

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
55 d ago

Exploit prediction

0.65% chance of exploitation in the next 30 days, higher than 51% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.0 9.8 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • libwebsockets libwebsockets

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.