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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.5 · 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 · score source

EPSS

• CVE-2026-30852: 0.47% estimated exploitation activity in the next 30 days; percentile 40.42 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The varsregexp matcher in vars.go:337 double-expands user-controlled input through the Caddy replacer. When varsregexp 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.DATABASEURL} or {file./etc/passwd} in a request header and the server will evaluate it, leaking environment variables, file contents, and system info. headerregexp does NOT do this — it passes header values straight to Match(). So this is a code-level inconsistency, not intended behavior. Details The bug is at modules/caddyhttp/vars.go, line 337 in MatchVarsRE.MatchWithError(): When the key is a placeholder like {http.request.header.X-Input}, repl.Get() resolves it to the raw header value (first expansion, line 318). Then repl.ReplaceAll() runs on that value again (second expansion, line 337), which evaluates any {env.}, {file.}, {system.} placeholders the…

Published by the source

6 Mar 2026, 23:40 UTC

Last modified by the source

9 Mar 2026, 15:51 UTC

Source last checked

26 Oct 2026, 15:15 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-m2w3-8f23-hxxf

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# Patch Next advisory brief: CVE-2026-30852

Advisory: Caddy's vars_regexp double-expands user input, leaking env vars and files
IDs: CVE-2026-30852, GHSA-m2w3-8f23-hxxf
Record: https://patchnext.com/advisories/cve-2026-30852 (revision 1, source checked 26 Oct 2026, 15:15 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/caddyserver/caddy/v2/modules/caddyhttp 2.11.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/caddyserver/caddy/v2/modules/caddyhttp: affected >= 2.7.5, <= 2.11.1; fixed in 2.11.2

## Suggested inspection (read-only)
- Go github.com/caddyserver/caddy/v2/modules/caddyhttp: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/caddyserver/caddy/v2/modules/caddyhttp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-m2w3-8f23-hxxf (GitHub-reviewed advisory GHSA-m2w3-8f23-hxxf lists affected ranges: Go github.com/caddyserver/caddy/v2/modules/caddyhttp >=2.7.5 <=2.11.1)

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