Exploiting XXE vulnerabilities in AMF libraries

[Nicolas Grégoire <nicolas.gregoire () agarri fr>]

Hello,

AMF (aka "Action Message Format") is a binary format used by Flash
applications communicating with server-side components. A few data types
supported by AMF deal with XML content (for example the "XML Document"
type in AMF0).

In 2015, several AMF libraries (including BlazeDS and PyAMF) were
identified as vulnerable to XXE (aka "XML External Entity") and SSRF
(aka "Server Side Forgery") attacks. I wrote a blog-post detailing:
- server-side exploitation of the PyAMF vulnerability
- server-side exploitation of the BlazeDS vulnerability
- client-side exploitation of the BlazeDS vulnerability

The article also includes a basic AMF client (in Python) used to exploit
these vulnerabilities (or interact with AMF gateways at large).

Link:
http://www.agarri.fr/kom/archives/2015/12/17/amf_parsing_and_xxe/index.html

Cheers,
Nicolas Grégoire

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