Uncaught Exception in undici - CVE-2026-109855
Published: October 14, 2026
Vulnerability identifier: #VU155785
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-109855
CWE-ID: CWE-248
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to an uncaught exception in undici's experimental WebSocket client when handling a failed WebSocket handshake over HTTP/2. A remote attacker can return a response that fails handshake validation from a malicious server and then destroy the connection to cause a denial of service.
Exploitation requires the client to connect to the malicious server with HTTP/2 support enabled through allowH2: true, which is the default setting.
Affected software
undici
How to mitigate CVE-2026-109855
Install security update from vendor's website.
undici - update to 8.11.2