CVE-2026-30852: Caddy: vars_regexp double-expands user input, leaking env vars and files

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-07 · updated 2026-06-17
Weakness: CWE-74

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.

Affected products

caddyserver caddy: from 2.7.5 before 2.11.2 — fixed in 2.11.2

How to fix

Upgrade to a fixed version: caddyserver caddy 2.11.2. Check the vendor advisory for mitigations.

References

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