CVE-2026-30852

Caddy: vars_regexp double-expands user input, leaking env vars and files

State: Published
Severity: 5.5 Medium
Published: Mar 7, 2026
Updated: Mar 9, 2026
Reserved: Mar 5, 2026

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.

Scores

CVSS	Score	Vector	Source
4.0	5.5 Medium	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:P	GitHub_M

Weaknesses

CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

Affected Products

Product	Versions
caddycaddyserver	>= 2.7.5, < 2.11.2Affected

References

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