Quick answers
- Is CVE-2026-19773 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-19773 being exploited in the wild.
- How severe is CVE-2026-19773?
- Critical severity, with a CVSS score of 9.8, published 15 September 2026.
- Which products and versions are affected?
- libwebsockets libwebsockets.
- Is there a fix for CVE-2026-19773?
- A patch was published on 2026-08-24: Coordinated public release and patch available Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-19773 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-19773?
- Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The vulnerability exists in the HTTP/2 HPACK path header parsing logic within lib/roles/h2/hpack.c. The root cause is insufficient validation of user-supplied header data, leading to an out-of-bounds write in the allocated header buffer. The flaw occurs in the lws_frag_append() function, which did not check if the buffer position exceeded the maximum allowed header data size before writing. An attacker can exploit this via a crafted HTTP/2 request sent over the network without authentication. The exploit allows arbitrary code execution in the context of the libwebsockets process. A patch is available in the upstream repository that adds bounds checking before the buffer write operation.
Affected products
- libwebsockets libwebsockets
Timeline
- 2026-07-03: disclosed: Vulnerability reported to vendor
- 2026-08-24: patched: Coordinated public release and patch available
- 2026-08-24: advisory: ZDI-26-590 advisory published