XML External Entity (XXE) Injection Affecting org.apache.flex.blazeds:flex-messaging-core Open this link in a new tab package, versions [,4.7.1)
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19 Aug 2015
19 Aug 2015
How to fix?
org.apache.flex.blazeds:flex-messaging-core to version 4.7.1 or higher.
org.apache.flex.blazeds:flex-messaging-core is a flex messaging core component for blazDS
Affected versions of this package are vulnerable to XML External Entity (XXE) Injection. A remote attacker could read arbitrary files via an AMF message containing an XML external entity declaration in conjunction with an entity reference. An AMF message (Action Message Format) is a binary format used to serialize object graphs such as ActionScript objects and XML. The
readBody method is used to parse the body of the AMF message,which in turn deserializes the message. Under certain conditions, the body is sent to be parsed in the
readXml() method as a UTF string.
xml string is then used to build a Document, via the
DocumentBuilder, by using the
stringToDocument method. The
DocumentBuilder allows external entities by default, resulting in the possible XML External Entity (XXE) injection.
XXE Injection is a type of attack against an application that parses XML input. XML is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. By default, many XML processors allow specification of an external entity, a URI that is dereferenced and evaluated during XML processing. When an XML document is being parsed, the parser can make a request and include the content at the specified URI inside of the XML document.
Attacks can include disclosing local files, which may contain sensitive data such as passwords or private user data, using file: schemes or relative paths in the system identifier.
For example, below is a sample XML document, containing an XML element- username.
<xml> <?xml version="1.0" encoding="ISO-8859-1"?> <username>John</username> </xml>
An external XML entity -
xxe, is defined using a system identifier and present within a DOCTYPE header. These entities can access local or remote content. For example the below code contains an external XML entity that would fetch the content of
/etc/passwd and display it to the user rendered by
<xml> <?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE foo [ <!ENTITY xxe SYSTEM "file:///etc/passwd" >]> <username>&xxe;</username> </xml>
Other XXE Injection attacks can access local resources that may not stop returning data, possibly impacting application availability and leading to Denial of Service.