Vulnerability · Published Nov 5, 2026 · Assigned by GitHub_M
CVE-2026-55458Caddy: RFC 7230 §6.1 compliance issue / Hop-by-hop headers that leak through
Low 2.9
In plain English
A low-severity security flaw in caddy from caddyserver. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.5, the reverse proxy's finalizeResponse method in modules/caddyhttp/reverseproxy/reverseproxy.go handles an upstream 101 Switching Protocols response before running removeConnectionHeaders and the hopHeaders deletion loop used for ordinary responses. The early return invokes handleUpgradeResponse, which copies the upstream headers to the client and normalizes only WebSocket-specific header names. An attacker who controls or compromises a proxied WebSocket upstream can therefore cause hop-by-hop headers such as Alt-Svc, Keep-Alive, and Proxy-Authenticate, as well as headers named by Connection, to cross the proxy boundary. For HTTP/2 or HTTP/3 extended CONNECT, the upstream 101 response may be represented to the client as an ordinary successful response, increasing the chance that leaked headers are processed. This issue is fixed in version 2.11.5.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | caddy | no fix listed | DEBIAN-CVE-2026-55458 |
| Debian:13 | caddy | no fix listed | DEBIAN-CVE-2026-55458 |
| Debian:14 | caddy | no fix listed | DEBIAN-CVE-2026-55458 |
| Go | github.com/caddyserver/caddy/v2 | 2.11.5 | GHSA-8qx7-j2v2-x6q5 |
| Go | github.com/caddyserver/caddy/v2 | 2.11.5 | GO-2026-6874 |
| Ubuntu:26.10 | caddy | no fix listed | UBUNTU-CVE-2026-55458 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| caddyserver | caddy | < 2.11.5 |
Weakness: CWE-444 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P