Weakness · High
CWE-185: Incorrect Regular Expression
What it is
The product specifies a regular expression in a way that causes data to be improperly matched or compared.
- Severity (our rating)
- High
- Likelihood of exploit
- Not rated by MITRE
- Introduced during
- Implementation
- Exploited in the wild
- No CVE in CISA's catalog
In more detail
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.
What an attacker can do
- Unexpected State (Other)
- Varies by Context (Other)
- Bypass Protection Mechanism (Access Control)
How to prevent it
Architecture and Design
- 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.
How to find it
- Automated Static Analysis. Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
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Start freeSource: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.