# 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:** JavaScript

- Prevalence: 中 覆盖 3 种语言
- Impact: 高 1 条严重级别为高的规则
- Prevention: 已记录 3 个修复示例

**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

基于 1 条 Shoulder 检测规则的 ReDoS 预防策略。

### JavaScript

Avoid nested quantifiers in regex and validate input length before matching

## Warning Signs

- [HIGH] potentially catastrophic regular expressions that could lead to ReDoS attacks

## Consequences

- 拒绝服务 (DoS)

## Mitigations

- 在正则表达式中避免嵌套量词和相互重叠的择一项
- 为正则表达式使用超时机制
- 考虑使用不回溯(non-backtracking)的正则引擎

## Detection

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

## Rules by Language

### Javascript (1 rules)

- **Regular Expression Denial of Service (ReDoS)** [HIGH]: Detects potentially catastrophic regular expressions that could lead to ReDoS attacks.

ReDoS occurs when regular expressions with certain patterns cause exponential backtracking,
leading to excessive CPU consumption. Evil regexes typically contain:

1. Nested quantifiers (e.g., (a+)+, (a*)*)
2. Alternation with overlapping patterns (e.g., (a|ab)*, (a|a)*)
3. Grouping with repetition where the group can match the same input in multiple ways
4. Complex patterns with overlapping possibilities that
  - Remediation: Avoid nested quantifiers and use safe regex libraries:

```javascript
const safeRegex = require('safe-regex');

if (!safeRegex(pattern)) {
  return res.status(400).json({ error: 'Invalid regex' });
}

if (input.length > 1000) {
  return res.status(400).json({ error: 'Input too long' });
}

const result = input.match(/^[a-zA-Z0-9]+$/);
```

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

### Typescript (1 rules)

- **Regular Expression Denial of Service (ReDoS)** [HIGH]: Detects potentially catastrophic regular expressions that could lead to ReDoS attacks.

ReDoS occurs when regular expressions with certain patterns cause exponential backtracking,
leading to excessive CPU consumption. Evil regexes typically contain:

1. Nested quantifiers (e.g., (a+)+, (a*)*)
2. Alternation with overlapping patterns (e.g., (a|ab)*, (a|a)*)
3. Grouping with repetition where the group can match the same input in multiple ways
4. Complex patterns with overlapping possibilities that
  - Remediation: Avoid nested quantifiers and use safe regex libraries:

```javascript
const safeRegex = require('safe-regex');

if (!safeRegex(pattern)) {
  return res.status(400).json({ error: 'Invalid regex' });
}

if (input.length > 1000) {
  return res.status(400).json({ error: 'Input too long' });
}

const result = input.match(/^[a-zA-Z0-9]+$/);
```

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