CWE-185: Incorrect Regular Expression
Description
The product specifies a regular expression in a way that causes data to be improperly matched or compared.
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.
- Abstraction
- ClassAn abstract weakness, independent of any specific language or technology.
- Likelihood of exploit
- Not rated by MITRE
- Status
- Draft
Common consequences
- Other
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.
- Access Control
Bypass Protection Mechanism
In PHP, regular expression checks can sometimes be bypassed with a null byte, leading to any number of weaknesses.
Potential mitigations
- ImplementationRefactoring
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.