PHP External Variable Modification
Draft Variant
Structure: Simple
Description
A PHP application does not properly protect against the modification of variables from external sources, such as query parameters or cookies. This can expose the application to numerous weaknesses that would not exist otherwise.
Common Consequences 1
Scope: Integrity
Impact: Modify Application Data
Potential Mitigations 1
Phase: RequirementsImplementation
Carefully identify which variables can be controlled or influenced by an external user, and consider adopting a naming convention to emphasize when externally modifiable variables are being used. An application should be reluctant to trust variables that have been initialized outside of its trust boundary. Ensure adequate checking is performed when relying on input from outside a trust boundary. Do not allow your application to run with register_globals enabled. If you implement a register_globals emulator, be extremely careful of variable extraction, dynamic evaluation, and similar issues, since weaknesses in your emulation could allow external variable modification to take place even without register_globals.
Observed Examples 5
CVE-2000-0860File upload allows arbitrary file read by setting hidden form variables to match internal variable names.
CVE-2001-0854Mistakenly trusts $PHP_SELF variable to determine if include script was called by its parent.
CVE-2002-0764PHP remote file inclusion by modified assumed-immutable variable.
CVE-2001-1025Modify key variable when calling scripts that don't load a library that initializes it.
CVE-2003-0754Authentication bypass by modifying array used for authentication.
Applicable Platforms
Languages:
PHP : Undetermined
Modes of Introduction
Implementation
Related Attack Patterns
Related Weaknesses
Taxonomy Mapping
- PLOVER
Notes
RelationshipThis is a language-specific instance of Modification of Assumed-Immutable Data (MAID). This can be resultant from direct request (alternate path) issues. It can be primary to weaknesses such as PHP file inclusion, SQL injection, XSS, authentication bypass, and others.