CAPEC-4 Using Alternative IP Address Encodings

This attack relies on the adversary using unexpected formats for representing IP addresses. Networked applications may expect network location information in a specific format, such as fully qualified domains names (FQDNs), URL, IP address, or IP Address ranges. If the location information is not validated against a variety of different possible encodings and formats, the adversary can use an alternate format to bypass application access control.

1. [Explore] [Survey the application for IP addresses as user input] Using a browser, an automated tool or by inspecting the application, an adversary records all entry points to the application where IP addresses are used. 2. [Experiment] [Probe entry points to locate vulnerabilities] The adversary uses the entry points gathered in the "Explore" phase as a target list and attempts alternate IP address encodings, observing application behavior. The adversary will also attempt to access the application through an alternate IP address encoding to see if access control changes 3. [Exploit] [Bypass access control] Using an alternate IP address encoding, the adversary will either access the application or give the alternate encoding as input, bypassing access control restrictions.

• The target software must fail to anticipate all of the possible valid encodings of an IP/web address. • The adversary must have the ability to communicate with the server.

• [Low] The adversary has only to try IP address format combinations.

• Confidentiality, Access Control, Authorization: Gain Privileges

• Design: Default deny access control policies • Design: Input validation routines should check and enforce both input data types and content against a positive specification. In regards to IP addresses, this should include the authorized manner for the application to represent IP addresses and not accept user specified IP addresses and IP address formats (such as ranges) • Implementation: Perform input validation for all remote content.