CWE-185: Incorrect Regular Expression
The product specifies a regular expression in a way that causes data to be improperly matched or compared.
How it's found
Incorrect Regular Expression describes a general pattern rather than a single fixed bug. Testers use a mix of static analysis and manual code review to find where a target's code matches this pattern, then confirm exploitability by hand.
When the regular expression is used in protection mechanisms such as filtering or validation, this may allow an attacker to bypass the intended restrictions on the incoming data.
Consequences
- Unexpected State, Varies by Context: When the regular expression is not correctly specified, data might have a different format or type than the rest of the program expects, producing resultant weaknesses or errors.
- Bypass Protection Mechanism: In PHP, regular expression checks can sometimes be bypassed with a null byte, leading to any number of weaknesses.
Mitigations
- Implementation: Regular expressions can become error prone when defining a complex language even for those experienced in writing grammars. Determine if several smaller regular expressions simplify one large regular expression. Also, subject the regular expression to thorough testing techniques such as equivalence partitioning, boundary value analysis, and robustness. After testing and a reasonable confidence level is achieved, a regular expression may not be foolproof. If an exploit is allowed to slip through, then record the exploit and refactor the regular expression.
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-185?
The product specifies a regular expression in a way that causes data to be improperly matched or compared.
How do you find Incorrect Regular Expression?
Incorrect Regular Expression describes a general pattern rather than a single fixed bug. Testers use a mix of static analysis and manual code review to find where a target's code matches this pattern, then confirm exploitability by hand.
What is the impact of CWE-185?
Unexpected State, Varies by Context: When the regular expression is not correctly specified, data might have a different format or type than the rest of the program expects, producing resultant weaknesses or errors. Bypass Protection Mechanism: In PHP, regular expression checks can sometimes be bypassed with a null byte, leading to any number of weaknesses.
Does TurboPentest test for Incorrect Regular Expression?
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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