Is Tomcat vulnerable to “Ghostcat” (CVE-2020-1938) via mod_proxy_ajp?

Is it possible to exploit the “Ghostcat” vulnerability (CNVD-2020-10487/CVE-2020-1938) indirectly over mod_proxy_ajp?

I was able to successfully test the proof-of-concept exploit (https://www.exploit-db.com/exploits/48143) when targeting my Tomcat’s AJP port. However, my tomcat instance is not directly externally accessible, but rather sits behind an Apache reverse proxy via mod_proxy_ajp. Am I safe from external Ghostcat attacks in this instance?

As a test for indirect exploitation, I sent an HTTP GET request targeting my Apache front-end which proxies to the Tomcat AJP port, and I set the following HTTP header:

req_attribute: javax.servlet.include.request_uri=/, javax.servlet.include.path_info=WEB-INF/web.xml, javax.servlet.include.servlet_path=/ 

I also tried variants of this header such as using semi-colons as a delimiter instead of commas, as well as having multiple req_attribute headers for each key,value pair on a separate line.

Fortunately, the body of the HTTP response did not dump my WEB-INF/web.xml file, therefore these indirect exploit attempts failed. Upon further inspection with tcpdump, I see that these req_attribute headers do not get encoded to AJP’s format of using a single byte (0x0a) to denote req_attribute. So it seems that the HTTP ASCII request headers do not translate into AJP’s binary request headers. Therefore I believe that the vulnerability is non-exploitable through HTTP requests that get passed to mod_proxy_ajp, is that correct? Or is there a clever way to craft an HTTP request that would make mod_proxy_ajp pass along the req_attribute headers in AJP’s binary format in order to indirectly exploit this vulnerability?

Tomcat AJP vulnerability CVE-2020-1938 aka Ghostcat

I have a question about Tomcat vulnerability CVE-2020-1938 aka Ghostcat. The security researcher who discovered the vulnerability created a write up here: https://www.chaitin.cn/en/ghostcat and a PoC here: https://github.com/YDHCUI/CNVD-2020-10487-Tomcat-Ajp-lfi.

Can this vulnerability still be exploited when Apache is acting as the reverse proxy for Tomcat (and communicating with it using AJP) or would it only work when communicating directly to the AJP service on Tomcat?

I can’t get the POC to work when using Apache as a proxy but I don’t know if that’s because of my lack of experience with Apache, Tomcat, and AJP and/or the lack of implementation in the POC to support exploitation over such a setup OR if the vulnerability is in fact only exploitable when communicating directly with the AJP service port 8009 on Tomcat.