CVE-2026-55458
Caddy: RFC 7230 §6.1 compliance issue / Hop-by-hop headers that leak through
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 4.0 | Low2.9 | 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 |
| NVDNVD · Received | 4.0 | Low2.9 | 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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
- EPSS (exploitation in 30 days)
- 0.50% · top 57% of all CVEs (6 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: Low 2.9.
Weakness
Affected products
- affected < 2.11.5
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- Gogithub.com/caddyserver/caddy/v2GHSA-8qx7-j2v2-x6q5 (opens in a new tab)
References (3)
- https://github.com/caddyserver/caddy/security/advisories/GHSA-8qx7-j2v2-x6q5 (opens in a new tab)x_refsource_CONFIRM
- https://github.com/caddyserver/caddy/commit/25b3eab6dbd8d2d2670711f26b774e0fd43e1179 (opens in a new tab)x_refsource_MISC
- https://github.com/caddyserver/caddy/releases/tag/v2.11.5 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-8qx7-j2v2-x6q5 (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-55458)Record last updated .