A critical unauthenticated remote code execution vulnerability was found in Apache Tapestry. The vulnerability found is a bypass of the fix for CVE-2019-0195. Before the fix of CVE-2019-0195 it was possible to download arbitrary class files from the classpath by providing a crafted asset file URL. An attacker was able to download the file
AppModule.class by requesting the URL
http://localhost:8080/assets/something/services/AppModule.class which contains a HMAC secret key. The fix for that bug was an ignore filter that checks if the URL ends with
.xml. Unfortunately, the ignore list solution can simply be bypassed by appending a
/ at the end of the URL
http://localhost:8080/assets/something/services/AppModule.class/ The slash is stripped after the ignore list check and the file
AppModule.class is loaded into the response. This class usually contains the HMAC secret key which is used to sign serialized Java objects. With the knowledge of that key an attacker can sign a Java gadget chain that leads to RCE (e.g.