# 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: Media 3 lenguajes cubiertos
- Impact: Alto 1 reglas de severidad alta
- Prevention: Documentada 3 ejemplos de corrección

**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

Estrategias de prevención para ReDoS basadas en 1 reglas de detección de Shoulder.

### Go

Avoid nested quantifiers in regex; use specific character classes instead

## Consequences

- DoS

## Mitigations

- Evita los cuantificadores anidados y las alternancias superpuestas en las regex
- Usa mecanismos de timeout en las regex
- Considera usar motores de regex sin retroceso (non-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