Buffer overflow in Libwebsockets
CVE-2026-19773
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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.006 (50.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 51st percentile — 50.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000
Affected products
- Libwebsockets — versions b4b5aed3903eaff09cd76a410f69bbe5dff66f8e
Weakness classification (CWE)
References
- www.zerodayinitiative.com/advisories/ZDI-26-590/ (x_research-advisory)
- github.com/warmcat/libwebsockets/commit/824151862f37bc72f46d9a3e01d5b9408d313a0b (vendor-advisory)
Frequently asked questions
- What is CVE-2026-19773?
- CVE-2026-19773 is a critical-severity vulnerability in Libwebsockets, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2026-09-15.
- How severe is CVE-2026-19773?
- Critical severity. CVSS v3 base score is 9.8 out of 10.