Inefficient Regular Expression Complexity (CWE-1333)

Inefficient Regular Expression Complexity

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

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.

Prevalence

Medium

3 languages covered

Impact

High

1 high-severity rules

Prevention

Documented

3 fix examples

2 Prevention

How to fix this vulnerability

Prevention strategies for ReDoS based on 3 Shoulder detection rules.

🐹 Go View all Go details →

Regular Expression Denial of Service MEDIUM

Avoid nested quantifiers in regex; use specific character classes instead

+1 -1 go

- re := regexp.MustCompile("(a+)+b")
+ re := regexp.MustCompile("^[a-z]+b$")

🟨 JavaScript View all JavaScript details →

Regular Expression Denial of Service (ReDoS) HIGH

Avoid nested quantifiers in regex and validate input length before matching

+6 -2 javascript

- const emailRegex = /^([a-zA-Z0-9]+\.)+[a-zA-Z]{2,}$/;
- if (emailRegex.test(req.body.email)) {
+ const validator = require('validator');
+ 
+ if (req.body.email.length > 254) {
+   return res.status(400).json({ error: 'Input too long' });
+ }
+ if (validator.isEmail(req.body.email)) {
    processEmail(req.body.email);
  }

🐍 Python View all Python details →

Regular Expression Denial of Service (ReDoS) MEDIUM

Replace nested quantifiers with simple patterns and bounded repetition

+1 -1 python

  import re
  
- email_pattern = re.compile(r'^([a-zA-Z0-9._-]+)+@[a-zA-Z0-9.-]+$')
+ email_pattern = re.compile(r'^[a-zA-Z0-9._-]{1,64}@[a-zA-Z0-9.-]{1,255}$')
  
  def validate_email(email):
      return email_pattern.match(email)

Key Practices

Use exponential time complexity when matching certain inputs

3 Detection

Find vulnerabilities in your code

Use Shoulder to scan your codebase for Inefficient Regular Expression Complexity patterns. 3 rules.

terminal

# Scan with Shoulder CLI
npx @shoulderdev/cli trust --cwe=1333

# Or scan entire project
npx @shoulderdev/cli trust .

Detection Rules (3)

🐹 Go 1 rules

Regular Expression Denial of Service MEDIUM

Regex pattern with nested quantifiers causes catastrophic backtracking.

🟨 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 cause catastrophic backtracking When user input is matched against these patterns, an attacker can craft input that causes the regex engine to take exponential time, effectively causing a denial of service.

🔷 Typescript 1 rules

Regular Expression Denial of Service (ReDoS) HIGH

🐍 Python 1 rules

Regular Expression Denial of Service (ReDoS) MEDIUM

Detects regular expressions with catastrophic backtracking patterns that can cause exponential time complexity when matching certain inputs. Attackers can exploit this to cause denial of service. Use simpler patterns or set timeouts.

4 Warning Signs

What to watch for in code reviews

These patterns indicate potential Inefficient Regular Expression Complexity vulnerabilities. Look for these during code reviews and security audits.

🟠

potentially catastrophic regular expressions that could lead to ReDoS attacks javascript-regex-dos

🟡

regular expressions with catastrophic backtracking patterns that can cause exponential time complexi python-redos

🔍

Scan your codebase for Inefficient Regular Expression Complexity

Shoulder CLI finds vulnerable patterns across your entire codebase.

npx shoulder trust Browse all rules