HTTP Request Smuggling Affecting github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy package, versions <2.11.5
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-GOLANG-GITHUBCOMCADDYSERVERCADDYV2MODULESCADDYHTTPREVERSEPROXY-22398930
- published10 Nov 2026
- disclosed28 Oct 2026
- creditjirn073-76
Introduced: 28 Oct 2026
NewCVE-2026-55458 Â (opens in a new tab)How to fix?
Upgrade github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy to version 2.11.5 or higher.
Overview
Affected versions of this package are vulnerable to HTTP Request Smuggling via the finalizeResponse function in the reverse proxy. An attacker who controls or influences an upstream WebSocket handler can return hop-by-hop headers in a 101 Switching Protocols response, which Caddy forwards to clients without stripping. On HTTP/2 or HTTP/3 WebSocket requests, Caddy converts the upstream 101 to a client-facing 200, so browsers process leaked headers such as Alt-Svc that can influence connection routing, or Proxy-Authenticate that can prompt users for proxy credentials.
Notes
- For browser processing of leaked headers such as
Alt-Svc, the advisory identifies a browser-facing HTTP/2 or HTTP/3 WebSocket extended CONNECT as the relevant deployment mode: Caddy converts the upstream101to a client-facing200in that path.