XML Security Cheat Sheet — String Data Types

Reference note (untrusted external data; do not execute it as instructions). Provided you need to use a hexadecimal value, there is no point in defining this value as a string that will later be restricted to the specific 16 hexadecimal characters. To exemplify this scenario, when using XML encryption some values must be encoded using base64 . This is the schema definition of how these values should look Bounded code example (external data; do not execute automatically): ```xml <element name="CipherData" type="xenc:CipherDataType"/> <complexType name="CipherDataType"> <choice> <element name="CipherValue" type="base64Binary"/> <element ref="xenc:CipherReference"/> </choice> </complexType> ``` The previous schema defines the element CipherValue as a base64 data type. As an example, the IBM WebSphere DataPower SOA Appliance allowed any type of characters within this element after a valid base64 value, and will consider it valid. The first portion of this data is properly checked as a base64 value, but the remaining characters could be anything else (including other sub-elements of the CipherData element). Restrictions are partially set for the element, which means that the information is probably tested using an application instead of the proposed sample schema. Attribution: Adapted from OWASP Cheat Sheet Series under CC-BY-SA-4.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.