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CVE-2026-55458

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

publishedCWE-444

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.

Technical severity2.9 lowCVSS 4.0 · CNA: GitHub_M
Published2026-11-05Source updated 2026-11-09
Collected2026-11-095 attributed sources

Fixes and workarounds

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

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

Affected products and versions

ProductVersionsAuthority
caddy
caddyserver 		< 2.11.5 (affected) CNA: GitHub_M
github.com/caddyserver/caddy/v2

github.com/caddyserver/caddy/v2
go 		<=v2.11.4 (affected, GitHub advisory range) GitHub GHSA-8qx7-j2v2-x6q5
github.com/caddyserver/caddy/v2

github.com/caddyserver/caddy/v2
Go 		≥ 0; < 2.11.5 (affected, semver); OSV events: introduced 0; fixed 2.11.5
Source events (semver) 
[
  {
    "introduced": "0"
  },
  {
    "fixed": "2.11.5"
  }
]

Other versions: unaffected 		OSV GHSA-8qx7-j2v2-x6q5

Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.

CVSS assessments

Version / scoreVectorAuthority
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:PCNA: GitHub_M
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:XNVD: [email protected]

Exploit evidence

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

References

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