Cross-site Scripting (XSS)

Affecting statics-server package, ALL versions

high severity

Overview

Affected versions of statics-server are vulnerable to Cross-site Scripting (XSS) attacks. It does not implement any HTML escaping when displays directory index in the browser. Variable v is used in <a href> element without escaping, which allows to embed HTML <iframe> tag with src attribute points to another HTML file in the directory. This file can contain malicious JavaScript code.

PoC by bl4de

    if(fs.lstatSync(staticPath).isDirectory()){
        var files=fs.readdirSync(staticPath);
        var lis='';
        files.forEach((v,i)=>{
            if(fs.lstatSync(path.resolve(staticPath,v)).isDirectory()){
                lis+=`<li><a href="${req.url}${v}/">${v}/</a></li>`;
            }else {
                lis+=`<li><a href="${req.url}${v}">${v}</a></li>`
            }
        });

        (...)

Details

Cross-Site Scripting (XSS) attacks occur when an attacker tricks a user’s browser to execute malicious JavaScript code in the context of a victim’s domain. Such scripts can steal the user’s session cookies for the domain, scrape or modify its content, and perform or modify actions on the user’s behalf, actions typically blocked by the browser’s Same Origin Policy.

These attacks are possible by escaping the context of the web application and injecting malicious scripts in an otherwise trusted website. These scripts can introduce additional attributes (say, a "new" option in a dropdown list or a new link to a malicious site) and can potentially execute code on the clients side, unbeknown to the victim. This occurs when characters like < > " ' are not escaped properly.

There are a few types of XSS:

  • Persistent XSS is an attack in which the malicious code persists into the web app’s database.
  • Reflected XSS is an which the website echoes back a portion of the request. The attacker needs to trick the user into clicking a malicious link (for instance through a phishing email or malicious JS on another page), which triggers the XSS attack.
  • DOM-based XSS is an that occurs purely in the browser when client-side JavaScript echoes back a portion of the URL onto the page. DOM-Based XSS is notoriously hard to detect, as the server never gets a chance to see the attack taking place.

Remediation

There is no fix version for statics-server.

References

Do your applications use this vulnerable package?

Credit
bl4de
CVE
CVE-2018-3771
CWE
CWE-79
Snyk ID
npm:statics-server:20180714
Disclosed
14 Jul, 2018
Published
23 Jul, 2018