CWE-627 Detail

In a language where the user can influence the name of a variable at runtime, if the variable names are not controlled, an attacker can read or write to arbitrary variables, or access arbitrary functions.

The resultant vulnerabilities depend on the behavior of the application, both at the crossover point and in any control/data flow that is reachable by the related variables or functions.

Background Details

Many interpreted languages support the use of a "$$varname" construct to set a variable whose name is specified by the $varname variable. In PHP, these are referred to as "variable variables." Functions might also be invoked using similar syntax, such as $$funcname(arg1, arg2).

Modes Of Introduction

Implementation

Applicable Platforms

Language

Name: PHP (Undetermined)
Name: Perl (Undetermined)

Common Consequences

Observed Examples

Potential Mitigations

Phases : Implementation
Refactor the code to avoid dynamic variable evaluation whenever possible.
Phases : Implementation
Use only allowlists of acceptable variable or function names.
Phases : Implementation
For function names, ensure that you are only calling functions that accept the proper number of arguments, to avoid unexpected null arguments.

Vulnerability Mapping Notes

Justification : This CWE entry is at the Variant level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comment : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

NotesNotes

Under-studied, probably under-reported. Few researchers look for this issue; most public reports are for PHP, although other languages are affected. This issue is likely to grow in PHP as developers begin to implement functionality in place of register_globals.

References

REF-517

Dynamic Evaluation Vulnerabilities in PHP applications
Steve Christey.
https://seclists.org/fulldisclosure/2006/May/35

REF-518

A Study In Scarlet: Exploiting Common Vulnerabilities in PHP Applications
Shaun Clowes.
https://securereality.com.au/study-in-scarlett/

Submission

Modifications