CVE-2020-9484 — PersistentManager Java deserialization vulnerability

This attack can have high impact (RCE), but the conditions that need to be met make the likelihood of exploitation low.

1. PersistentManager needs to be enabled manually by the tomcat administrator. This is likely to happen only on websites with high traffic loads (but not too high, as it will be more likely that a JDBC Store is used instead of a File Store)
   
2. The attacker has to find a separate file upload vulnerability to place the malicious serialized file on the server.
   
3. There have to be libraries on the classpath which are vulnerable to be exploited by a Java deserialization attack (e.g. gadgets).
   

However, a large range of versions of tomcat are affected.

More info in this article: https://www.redtimmy.com/java-hacking/apache-tomcat-rce-by-deserialization-cve-2020-9484-write-up-and-exploit/

@cblack-r7 and I looked at this a couple weeks ago, specifically https://seclists.org/oss-sec/2020/q2/136 and https://github.com/IdealDreamLast/CVE-2020-9484. I did a double take because I thought it included a file write. Not so. There are a handful of prerequisites that mitigate the impact of this vulnerability.

If the stars align, this could be valuable, since Tomcat is everywhere. But I don’t think it’s worth writing an exploit for this, beyond a PoC, since exploitation is so niche. @redtimmy’s writeup is most excellent. Go read that.