Description
Caddy is an extensible server platform that uses TLS by default. From version 2.7.5 to before version 2.11.2, the vars_regexp matcher in vars.go:337 double-expands user-controlled input through the Caddy replacer. When vars_regexp matches against a placeholder like {http.request.header.X-Input}, the header value gets resolved once (expected), then passed through repl.ReplaceAll() again (the bug). This means an attacker can put {env.DATABASE_URL} or {file./etc/passwd} in a request header and the server will evaluate it, leaking environment variables, file contents, and system info. This issue has been patched in version 2.11.2.
Problem types
CWE-200: Exposure of Sensitive Information to an Unauthorized Actor
Product status
References
github.com/.../caddy/security/advisories/GHSA-m2w3-8f23-hxxf
github.com/caddyserver/caddy/pull/5408
github.com/caddyserver/caddy/releases/tag/v2.11.2