The product uses external input to determine the names of variables into which information is extracted, without verifying that the names of the specified variables are valid. This could cause the program to overwrite unintended variables.
Extended Description
For example, in PHP, calling extract() or import_request_variables() without the proper arguments could allow arbitrary global variables to be overwritten, including superglobals. Similar functionality might be possible in other interpreted languages, including custom languages.
Alternate Terms
Variable overwrite
Time of Introduction
Implementation
Applicable Platforms
Languages
PHP
Common Consequences
Scope
Effect
Integrity
Technical Impact: Modify application
data
An attacker could modify sensitive data or program variables.
Demonstrative Examples
Example 1
This code uses the credentials sent in a POST request to login a
user.
(Bad Code)
Example
Language: PHP
//Log user in, and set $isAdmin to true if user is an
administrator
The call to extract() will overwrite the existing values of any
variables defined previously, in this case $isAdmin. An attacker can
send a POST request with an unexpected third value "isAdmin" equal to
"true", thus gaining Admin privileges.
import_request_variables() buried in include files
makes post-disclosure analysis confusing
Potential Mitigations
Phase: Implementation
Strategy: Input Validation
Use whitelists of variable names that can be extracted.
Phase: Implementation
Consider refactoring your code to avoid extraction routines
altogether.
Phase: Implementation
In PHP, call extract() with options such as EXTR_SKIP and
EXTR_PREFIX_ALL; call import_request_variables() with a prefix argument.
Note that these capabilities are not present in all PHP versions.
Other Notes
In general, variable extraction can make control and data flow analysis
difficult to perform. For PHP, extraction can be used to provide
functionality similar to register_globals, which is frequently disabled in
production systems. Many PHP versions will overwrite superglobals in
extract/import_request_variables calls.
Weakness Ordinalities
Ordinality
Description
Primary
(where
the weakness exists independent of other weaknesses)
Description
