CVE-2026-55458

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-11-05 21:18 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-11-05 21:18 UTC Last updatedMost recent change to the record

Details

Published

2026-11-05 21:18 UTC

Last modified

2026-11-05 21:18 UTC

Weakness

CWE-444

Record status

Received

Attack profile CVSS 4.0 · 2.9

Attack vector

Network

Complexity

Low

Attack requirements

Present

Privileges needed

None

User interaction

None

Confidentiality

None

Integrity

Low

Availability

None