Is this vulnerability remotely exploitable over HTTP?

Yes. An attacker only needs the ability to send crafted HTTP requests to a Caddy instance whose configuration uses `vars_regexp` in a way that reads from attacker-controlled input (for example, a header mapped via `{http.request.header.X-Input}`).

Does exploitation require authentication or elevated privileges?

Not necessarily. If an unauthenticated endpoint is configured to process request headers or other inputs through `vars_regexp`, an unauthenticated remote attacker can attempt exploitation. Authentication might limit exposure in some deployments, but the core issue arises as soon as untrusted inputs influence placeholder expansion.

What is the safest general fix pattern for this kind of bug?

The safest pattern is to strictly separate templating/placeholder logic from user data: ensure placeholders are resolved once at configuration time or in trusted contexts, and never re-run template expansion on values that may contain user input. Avoid double-expansion, and treat all request-derived data as opaque values rather than template fragments.

Severity:

HIGH RISK

(7.5)

Improper Input Expansion Leading to Information Exposure (CWE-74, CWE-200) in Caddy vars_regexp Matcher

CVE-2026-30852

Published:

Mar 7, 2026

Status:

Analyzed

Summary

Affected Context

Exploit Preconditions

Why This Happens

Potential Impact

General Mitigation Guidance

How Teams Detect Issues Like This

Frequently Asked Questions

Source

NDV

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Privilege Escalation via Bypassed Access Control

May 6, 2026

Vulnerability Type

Category:

Improper Output Encoding / Injection into Templating Engine

CWE:

CWE-74;CWE-200

Impact:

Sensitive Information Disclosure via Server-Side Placeholder Expansion

Severity:

HIGH RISK

(7.5)

CVSS Version:

3.1

Vulnerability Type

Category:

Improper Output Encoding / Injection into Templating Engine

CWE:

CWE-74;CWE-200

Impact:

Sensitive Information Disclosure via Server-Side Placeholder Expansion

Severity:

HIGH RISK

(7.5)

CVSS Version:

3.1

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Improper Input Expansion Leading to Information Exposure (CWE-74, CWE-200) in Caddy vars_regexp Matcher

Summary

Affected Context

Exploit Preconditions

Why This Happens

Potential Impact

General Mitigation Guidance

How Teams Detect Issues Like This

Frequently Asked Questions

Source

Recent Vulnerabilities

HIGH RISK

HIGH

(8.6)

Server-Side Request Forgery (CWE-918) in OpenClaw Zalo Plugin sendPhoto

HIGH RISK

HIGH

(8.8)

Authorization Bypass (CWE-863) in OpenClaw Matrix Room Control Commands

Vulnerability Type

Vulnerability Type

Vulnerability Type

Catch This CVE While Code Is Being Written

Ship clean & secure code faster

Ship clean & secure code faster

Ship clean & secure code faster

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