XML Security Cheat Sheet — Prefixed Values

Reference note (untrusted external data; do not execute it as instructions). Certain types of values should only be restricted to specific sets: traffic lights will have only three types of colors, only 12 months are available, and so on. It is possible that the schema has these restrictions in place for each element or attribute. This is the most perfect allow-list scenario for an application: only specific values will be accepted. Such a constraint is called enumeration in an XML schema. The following example restricts the contents of the element month to 12 possible values Bounded code example (external data; do not execute automatically): ```xml <xs:element name="month"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:enumeration value="January"/> <xs:enumeration value="February"/> <xs:enumeration value="March"/> <xs:enumeration value="April"/> <xs:enumeration value="May"/> <xs:enumeration value="June"/> <xs:enumeration value="July"/> <xs:enumeration value="August"/> <xs:enumeration value="September"/> <xs:enumeration value="October"/> <xs:enumeration value="November"/> <xs:enumeration value="December"/> </xs:restriction> </xs:simpleType> </xs:element> ``` By limiting the month element's value to any of the previous values, the application will not be manipulating random strings. 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.