Inconsistent interpretation of HTTP requests in Caddy - CVE-2026-55458
Published: November 9, 2026
Vulnerability identifier: #VU163184
CSH Severity: Low
CVSS v4: 4.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:A/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-55458
CWE-ID: CWE-444
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows an attacker controlling an upstream server to inject hop-by-hop headers into responses forwarded to clients.
The vulnerability exists due to missing hop-by-hop header filtering in Caddy's reverse proxy when processing upstream WebSocket upgrade responses. An attacker controlling an upstream server can supply crafted headers in a 101 Switching Protocols response that reach a client initiating a proxied WebSocket connection.
Affected software
Caddy
How to mitigate CVE-2026-55458
Install security update from vendor's website.
Caddy - update to 2.11.5