CWE-473: PHP External Variable Modification
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.
How it's found
PHP External Variable Modification is a specific, narrowly defined instance of a broader pattern. Testers confirm it with targeted code review and a proof-of-concept input that exercises the exact code path this weakness describes.
Consequences
- Modify Application Data
Mitigations
- Requirements/Implementation: 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.
Where this fits in a TurboPentest engagement
This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.
Frequently asked questions
What is CWE-473?
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.
How do you find PHP External Variable Modification?
PHP External Variable Modification is a specific, narrowly defined instance of a broader pattern. Testers confirm it with targeted code review and a proof-of-concept input that exercises the exact code path this weakness describes.
What is the impact of CWE-473?
Modify Application Data
Does TurboPentest test for PHP External Variable Modification?
This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.
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Written and reviewed by
Michel Chamberland - Founder & CEO, IntegSec
CISSP, OSCP, OSCE, CEH, GIAC, CCSK · 20+ years in offensive security
Michel has spent 20+ years on offensive security teams including IBM X-Force Red and Trustwave SpiderLabs, leading penetration tests, red team engagements, and breach response for Fortune 500 customers. He is the founder of IntegSec and the architect of TurboPentest.
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