CWE-611Improper Restriction of XML External Entity Reference

Description

Common consequences· 3

• Confidentiality — Read Application Data, Read Files or Directories
  If the attacker is able to include a crafted DTD and a default entity resolver is enabled, the attacker may be able to access arbitrary files on the system. By submitting an XML file that defines an external entity with a file:// URI, an attacker can cause the processing application to read the contents of a local file. For example, a URI such as "file:///c:/winnt/win.ini" designates (in Windows) the file C:\Winnt\win.ini, or file:///etc/passwd designates the password file in Unix-based systems. Once the content of the URI is read, it is fed back into the application that is processing the XML. This application may echo back the data (e.g., in an error message), thereby exposing the file contents.
• Integrity — Bypass Protection Mechanism
  An attacker may supply a crafted DTD using URIs with schemes such as http://, forcing the application to make outgoing HTTP requests to servers that the attacker cannot reach directly, which can be used to bypass firewall restrictions; hide the source of attacks such as port scanning; or otherwise leverage the server's trust relationship with other entities.
• Availability — DoS: Resource Consumption (CPU), DoS: Resource Consumption (Memory)
  The product could consume excessive CPU cycles or memory using a URI that points to a large file, or a device that always returns data such as /dev/random. Alternately, the URI could reference a file that contains many nested or recursive entity references to further slow down parsing.

Potential mitigations· 1

• [Implementation, System Configuration]Many XML parsers and validators can be configured to disable external entity expansion.

Related CAPEC attack patterns· 1

Exploits (incoming)1

Compliance frameworks addressing this (incoming)1

(incoming)57

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Related by meaning· 6

Nearest entities by semantic similarity across the cs-graph corpus.