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

CVE-2026-19773 is fixed in 10 products on 1 platform, first by libwebsockets-evlib-ev 4.3.5-3ubuntu1.2+esm1, released September 15, 2026. It is not reported as exploited. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/cve/CVE-2026-19773
- Priority: Urgent
- CVSS: 9.8 (critical)
- EPSS: 0.0065
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 15, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libwebsockets Debian 13.5 (trixie) | 4.3.5-1+deb13u3 | [DEBIAN-CVE-2026-19773](https://patchblox.com/security/data/fix/linux/debian-cve-2026-19773.md) | Sep 30, 2026 |
| Linux | libwebsockets Debian 14 | 4.3.5-7 | [DEBIAN-CVE-2026-19773](https://patchblox.com/security/data/fix/linux/debian-cve-2026-19773.md) | Sep 30, 2026 |
| Linux | libwebsockets-evlib-ev Ubuntu 24.04.5 LTS (noble) | 4.3.3-1.1ubuntu0.1~esm3 | [libwebsockets-evlib-ev 4.3.3-1.1ubuntu0.1~esm3](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libwebsockets-evlib-ev-4.3.3-1.1ubuntu0.1-esm3.md) | Oct 8, 2026 |
| Linux | libwebsockets-evlib-ev Ubuntu 26.04.1 LTS (resolute) | 4.3.5-3ubuntu1.2+esm1 | [libwebsockets-evlib-ev 4.3.5-3ubuntu1.2+esm1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libwebsockets-evlib-ev-4.3.5-3ubuntu1.2-esm1.md) | Sep 15, 2026 |
| Linux | libwebsockets-evlib-glib Ubuntu 24.04.5 LTS (noble) | 4.3.3-1.1ubuntu0.1~esm3 | [libwebsockets-evlib-glib 4.3.3-1.1ubuntu0.1~esm3](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libwebsockets-evlib-glib-4.3.3-1.1ubuntu0.1-esm3.md) | Oct 8, 2026 |
| Linux | libwebsockets-evlib-glib Ubuntu 26.04.1 LTS (resolute) | 4.3.5-3ubuntu1.2+esm1 | [libwebsockets-evlib-glib 4.3.5-3ubuntu1.2+esm1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libwebsockets-evlib-glib-4.3.5-3ubuntu1.2-esm1.md) | Sep 15, 2026 |
| Linux | libwebsockets-evlib-uv Ubuntu 24.04.5 LTS (noble) | 4.3.3-1.1ubuntu0.1~esm3 | [libwebsockets-evlib-uv 4.3.3-1.1ubuntu0.1~esm3](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libwebsockets-evlib-uv-4.3.3-1.1ubuntu0.1-esm3.md) | Oct 8, 2026 |
| Linux | libwebsockets-evlib-uv Ubuntu 26.04.1 LTS (resolute) | 4.3.5-3ubuntu1.2+esm1 | [libwebsockets-evlib-uv 4.3.5-3ubuntu1.2+esm1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libwebsockets-evlib-uv-4.3.5-3ubuntu1.2-esm1.md) | Sep 15, 2026 |
| Linux | libwebsockets-test-server Ubuntu 18.04.6 LTS (bionic) | 2.0.3-3ubuntu0.1~esm1 | [libwebsockets-test-server 2.0.3-3ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libwebsockets-test-server-2.0.3-3ubuntu0.1-esm1.md) | Oct 8, 2026 |
| Linux | libwebsockets-test-server Ubuntu 20.04 LTS (focal) | 3.2.1-3ubuntu0.1~esm3 | [libwebsockets-test-server 3.2.1-3ubuntu0.1~esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libwebsockets-test-server-3.2.1-3ubuntu0.1-esm3.md) | Oct 8, 2026 |
| Linux | libwebsockets-test-server Ubuntu 22.04.1 LTS (jammy) | 4.0.20-2ubuntu1.1+esm2 | [libwebsockets-test-server 4.0.20-2ubuntu1.1+esm2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libwebsockets-test-server-4.0.20-2ubuntu1.1-esm2.md) | Oct 8, 2026 |
| Linux | libwebsockets-test-server Ubuntu 24.04.5 LTS (noble) | 4.3.3-1.1ubuntu0.1~esm3 | [libwebsockets-test-server 4.3.3-1.1ubuntu0.1~esm3](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libwebsockets-test-server-4.3.3-1.1ubuntu0.1-esm3.md) | Oct 8, 2026 |
| Linux | libwebsockets-test-server Ubuntu 26.04.1 LTS (resolute) | 4.3.5-3ubuntu1.2+esm1 | [libwebsockets-test-server 4.3.5-3ubuntu1.2+esm1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libwebsockets-test-server-4.3.5-3ubuntu1.2-esm1.md) | Sep 15, 2026 |
| Linux | libwebsockets-test-server-common Ubuntu 18.04.6 LTS (bionic) | 2.0.3-3ubuntu0.1~esm1 | [libwebsockets-test-server-common 2.0.3-3ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libwebsockets-test-server-common-2.0.3-3ubuntu0.1-esm1.md) | Oct 8, 2026 |
| Linux | libwebsockets-test-server-common Ubuntu 20.04 LTS (focal) | 3.2.1-3ubuntu0.1~esm3 | [libwebsockets-test-server-common 3.2.1-3ubuntu0.1~esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libwebsockets-test-server-common-3.2.1-3ubuntu0.1-esm3.md) | Oct 8, 2026 |
| Linux | libwebsockets-test-server-common Ubuntu 22.04.1 LTS (jammy) | 4.0.20-2ubuntu1.1+esm2 | [libwebsockets-test-server-common 4.0.20-2ubuntu1.1+esm2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libwebsockets-test-server-common-4.0.20-2ubuntu1.1-esm2.md) | Oct 8, 2026 |
| Linux | libwebsockets-test-server-common Ubuntu 24.04.5 LTS (noble) | 4.3.3-1.1ubuntu0.1~esm3 | [libwebsockets-test-server-common 4.3.3-1.1ubuntu0.1~esm3](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libwebsockets-test-server-common-4.3.3-1.1ubuntu0.1-esm3.md) | Oct 8, 2026 |
| Linux | libwebsockets-test-server-common Ubuntu 26.04.1 LTS (resolute) | 4.3.5-3ubuntu1.2+esm1 | [libwebsockets-test-server-common 4.3.5-3ubuntu1.2+esm1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libwebsockets-test-server-common-4.3.5-3ubuntu1.2-esm1.md) | Sep 15, 2026 |
| Linux | libwebsockets15 Ubuntu 20.04 LTS (focal) | 3.2.1-3ubuntu0.1~esm3 | [libwebsockets15 3.2.1-3ubuntu0.1~esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libwebsockets15-3.2.1-3ubuntu0.1-esm3.md) | Oct 8, 2026 |
| Linux | libwebsockets16 Ubuntu 22.04.1 LTS (jammy) | 4.0.20-2ubuntu1.1+esm2 | [libwebsockets16 4.0.20-2ubuntu1.1+esm2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libwebsockets16-4.0.20-2ubuntu1.1-esm2.md) | Oct 8, 2026 |
| Linux | libwebsockets19t64 Ubuntu 24.04.5 LTS (noble) | 4.3.3-1.1ubuntu0.1~esm3 | [libwebsockets19t64 4.3.3-1.1ubuntu0.1~esm3](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libwebsockets19t64-4.3.3-1.1ubuntu0.1-esm3.md) | Oct 8, 2026 |
| Linux | libwebsockets19t64 Ubuntu 26.04.1 LTS (resolute) | 4.3.5-3ubuntu1.2+esm1 | [libwebsockets19t64 4.3.5-3ubuntu1.2+esm1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libwebsockets19t64-4.3.5-3ubuntu1.2-esm1.md) | Sep 15, 2026 |
| Linux | libwebsockets8 Ubuntu 18.04.6 LTS (bionic) | 2.0.3-3ubuntu0.1~esm1 | [libwebsockets8 2.0.3-3ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libwebsockets8-2.0.3-3ubuntu0.1-esm1.md) | Oct 8, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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