CVE-2026-30852 Caddy: vars_regexp double-expands user input, leaking env vars and files
Attackers can leak environment variables and file contents by injecting placeholders into request headers processed by the vars_regexp matcher.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-30852?
CVE-2026-30852 is a medium-severity vulnerability in caddyserver caddy, published on 7 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-30852?
3 open source packages ship an affected version, including github.com/caddyserver/caddy/v2/modules/caddyhttp and github.com/caddyserver/caddy/v2. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/caddyserver/caddy/v2/modules/caddyhttp Go | From 2.7.5 | 2.11.2 |
github.com/caddyserver/caddy/v2/modules/caddyhttp Go | From 2.7.5 | 2.11.2 |
github.com/caddyserver/caddy/v2 Go | From 2.7.5 | 2.11.2 |
Products include Caddyserver Caddy.
How do I fix CVE-2026-30852?
Upgrade github.com/caddyserver/caddy/v2/modules/caddyhttp to 2.11.2 or later.
Is CVE-2026-30852 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-30852 exists.
Other vulnerabilities in caddyserver caddy
- CVE-2018-21246 Caddy vulnerable to Authentication Bypass due to mishandling of TLS client authentication
- CVE-2026-27590 Caddy: Unicode case-folding length expansion causes incorrect split_path index in FastCGI transport
- CVE-2026-27586 Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
- CVE-2026-45135 Caddy: Unsafe Unicode Handling in FastCGI splitPos Allows Execution of Non-PHP Files
- CVE-2026-52845 Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
Sources
Also known as GHSA-m2w3-8f23-hxxf, GO-2026-4644, MINI-6jp4-8pf3-mxf8, MINI-r36r-ph7f-97w4, UBUNTU-CVE-2026-30852.