# CVE-2026-55458: Caddy: RFC 7230 §6.1 compliance issue / Hop-by-hop headers that leak through

Status: published. Published: 2026-11-05. Updated: 2026-11-09.

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.

## Remediation

- fix: github.com/caddyserver/caddy/v2 (go): GitHub reports patched versions v2.11.5. Check the advisory for the affected release branch. (source: GitHub GHSA-8qx7-j2v2-x6q5) — https://github.com/caddyserver/caddy/security/advisories/GHSA-8qx7-j2v2-x6q5
- fix: github.com/caddyserver/caddy/v2 (Go): OSV reports a fixed version 2.11.5. Check the advisory for supported release branches. (source: OSV GHSA-8qx7-j2v2-x6q5) — https://github.com/advisories/GHSA-8qx7-j2v2-x6q5

## Affected products and versions

- caddyserver / caddy: < 2.11.5 (affected). Source: CNA: GitHub_M
-  / github.com/caddyserver/caddy/v2 (github.com/caddyserver/caddy/v2): <=v2.11.4 (affected, GitHub advisory range). Source: GitHub GHSA-8qx7-j2v2-x6q5
-  / github.com/caddyserver/caddy/v2 (github.com/caddyserver/caddy/v2): ≥ 0; < 2.11.5 (affected, semver); OSV events: introduced 0; fixed 2.11.5. Source: OSV GHSA-8qx7-j2v2-x6q5

## Severity and prioritization

- CVSS 4.0: 2.9 (low); 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; source: CNA: GitHub_M

- CVSS 4.0: 2.9 (low); 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; source: NVD: security-advisories@github.com

- CISA KEV: No listing in collected sources

- EPSS: 0.50% as of 2026-11-09; percentile 43.05%

- SSVC: exploitation poc; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-444

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/caddyserver/caddy/security/advisories/GHSA-8qx7-j2v2-x6q5 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/caddyserver/caddy/commit/25b3eab6dbd8d2d2670711f26b774e0fd43e1179 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/caddyserver/caddy/releases/tag/v2.11.5 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/caddyserver/caddy/commit/25b3eab6dbd8d2d2670711f26b774e0fd43e1179 (security-advisories@github.com)

- https://github.com/caddyserver/caddy/releases/tag/v2.11.5 (security-advisories@github.com)

- https://github.com/caddyserver/caddy/security/advisories/GHSA-8qx7-j2v2-x6q5 (security-advisories@github.com)

- https://github.com/caddyserver/caddy/security/advisories/GHSA-8qx7-j2v2-x6q5 (GitHub Security Advisories; advisory)

- https://github.com/advisories/GHSA-8qx7-j2v2-x6q5 (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-8qx7-j2v2-x6q5 (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-55458; retrieved 2026-11-09; source updated 2026-11-09

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55458; retrieved 2026-11-06; source updated 2026-11-05

- GitHub Security Advisories: https://github.com/caddyserver/caddy/security/advisories/GHSA-8qx7-j2v2-x6q5; retrieved 2026-11-07; source updated 2026-10-13

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-8qx7-j2v2-x6q5; retrieved 2026-11-09; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-55458; retrieved 2026-11-09; source updated Not reported

Revision: c7d76bc5c4c6611e91bf70360b9aa87b563da3269909973095b6895945953744

Canonical: https://y2.dev/cve/CVE-2026-55458

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