# Inefficient Regular Expression Complexity (CWE-1333)

The product uses a regular expression with an inefficient, possibly exponential worst-case computational complexity that consumes excessive CPU cycles.

**Stack:** Go

- Prevalence: Média 3 linguagens cobertas
- Impact: Alto 1 regras de severidade alta
- Prevention: Documentada 3 exemplos de correção

**OWASP:** Injection (A03:2021-Injection) - #3

## Description

Certain regular expression patterns can take exponential time to evaluate on certain inputs (ReDoS). Attackers can craft inputs that cause the regex engine to consume excessive CPU time, leading to denial of service.

## Prevention

Estratégias de prevenção para ReDoS baseadas em 1 regras de detecção do Shoulder.

### Go

Avoid nested quantifiers in regex; use specific character classes instead

## Consequences

- DoS

## Mitigations

- Evite quantificadores aninhados e alternâncias sobrepostas em regex
- Use mecanismos de timeout em regex
- Considere usar motores de regex sem backtracking

## Detection

- Total rules: 3
- Languages: go, javascript, typescript, python

## Rules by Language

### Go (1 rules)

- **Regular Expression Denial of Service** [MEDIUM]: Regex pattern with nested quantifiers causes catastrophic backtracking.
  - Remediation: Avoid nested quantifiers like (a+)+. Use possessive quantifiers or atomic groups.

```go
// Avoid patterns like: (a+)+, (.*)*
// Use specific patterns instead
re := regexp.MustCompile(`^[a-z]+$`)
```

Learn more: https://shoulder.dev/learn/go/cwe-1333/regex-dos