ACME Challenge Path Cross-Site Scripting Scanner

The ACME Challenge Path is a mechanism used in Automated Certificate Management Environments to prove control over a domain. It is widely used by hosting providers and web servers to automate the issuance of SSL/TLS certificates. The implementation involves serving specific files at well-known paths to prove domain ownership as part of the certificate validation process. Without proper sanitization, vulnerabilities such as Cross-Site Scripting can arise, compromising the security and integrity of the web application. This tool checks for XSS vulnerabilities specifically in the ACME http-01 challenge implementations, where sanitization issues may occur. Security teams and administrators can use this scanner to identify and remediate potential flaws within their ACME Challenge Path implementations.

The Cross-Site Scripting (XSS) vulnerability arises when web applications do not adequately sanitize user input or output. In the context of the ACME Challenge Path, XSS can occur if challenge keys from the URL are reflected without proper sanitization. This can lead to arbitrary JavaScript execution in the client's browser, which can be used to hijack sessions, redirect users, or perform actions on behalf of the victim. It's a serious security issue that potentially affects any poorly implemented web application feature that incorporates user input into the response. This scanner is designed to detect such vulnerabilities specifically in the ACME Challenge Path implementations.

The technical aspect of this scanner involves sending a crafted GET request to the ACME Challenge Path. The vulnerable endpoint is typically a URL path like `/.well-known/acme-challenge/`. The scanner injects a script payload designed to execute JavaScript when unescaped to verify if the endpoint reflects it back unsanitized. If the challenge key is improperly handled and executed in the browser, the scanner confirms the XSS vulnerability. This is detectable by checking for specific JavaScript execution from the body of the HTTP response.

Exploiting XSS vulnerabilities in the ACME Challenge Path can lead to a range of harmful effects. Attackers may execute arbitrary scripts in users' browsers, leading to session hijacking, data theft, and redirection to malicious sites. Such vulnerabilities can also be used to manipulate or deface content, perform phishing attacks, and extend control beyond the intended scope. Protecting against this requires diligent input sanitization and output escaping to prevent any malicious scripts from being executed through user input.

REFERENCES

• https://labs.detectify.com/security-guidance/xss-using-quirky-implementations-of-acme-http-01/
• https://www.acunetix.com/vulnerabilities/web/cross-site-scripting-in-http-01-acme-challenge-implementation/