Bypassing Rate Limiting: Understanding Techniques and Solutions
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Chapter 1: Introduction to Rate Limiting
When browsing a website and repeatedly sending requests in a short timeframe, you might be prompted to complete a captcha or provide additional verification. This mechanism is known as "Rate Limiting." It is activated when a site suspects that requests are being generated by a bot or automated tool. The primary purpose of rate limiting is to protect application resources, ensure optimal response times for users, and sometimes safeguard user accounts against brute-force attacks. Excessive requests can be exploited to crawl a website or abuse user logins, making it essential to implement rate limits.
What is Rate Limiting?
Rate limiting restricts the number of consecutive requests sent to a specific endpoint, helping to protect websites from denial-of-service (DoS) attacks and various other threats. This protective measure is crucial for functions like logging in, signing up, password recovery, and two-factor authentication. It also applies to scenarios such as applying coupon codes.
To illustrate, consider an application that authenticates users with a one-time password (OTP). Without rate limiting on that endpoint, an attacker could easily brute-force the OTP, potentially gaining access to a user's account.
Uses of Rate Limiting:
- Minimizes server load, enhancing performance and resource use.
- Reduces the risk of brute-force attacks on login, OTP verification, and password recovery.
- Lowers the chances of DoS attacks.
Why Do Attacks Occur?
Login functionality is a standard feature across applications, allowing users to access their accounts via passwords or OTPs. Given the numerous data breaches in recent years, many usernames and passwords have been compromised. Without proper rate limiting, attackers can exploit these credentials to access accounts. Even with OTPs in place, brute-force attacks can still be executed.
Bypassing Rate Limiting Protections
If a website implements rate limiting, it can sometimes be bypassed through specific headers or IP rotation, especially if the implementation is flawed. Here are some common techniques:
Using Headers in Requests
Certain headers can be manipulated to evade rate limits. For instance:
- X-Forwarded-Host: This header indicates the hostname used for the request. In environments with reverse proxies, multiple hostnames may be used, which could aid in bypassing rate limits if manipulated appropriately.
- X-Forwarded-For: This header reveals the original IP address of the requester. By altering this header's value, an attacker can present multiple IP addresses, potentially evading detection and circumventing rate limits.
Other Bypass Methods
An attacker can also bypass rate limits by appending a "Space" or "Null Byte" to the username during login attempts. This can cause the backend to truncate the input, allowing the attacker to evade restrictions.
Utilizing IP Rotation with Burp Suite
Burp Suite, particularly its enterprise version, offers an IP Rotation feature that allows attackers to change their source IP for each request, thus bypassing rate limiting based on IP address.
Remediation Strategies
Password Complexity: Encourage users to create longer, more complex passwords (at least 8-16 characters, including letters, numbers, and symbols) to bolster security against brute-force attacks.
Limiting Login Attempts: Implementing restrictions on the number of login attempts can significantly mitigate risks. Once the limit is reached, consider temporarily locking the account and blocking the offending IP.
Conclusion
Applying rate limiting effectively can safeguard applications against DoS attacks and brute-force attempts. It is crucial to maintain these protections, as inadequate implementation could lead to compromised user accounts and potential spam issues.
This first video provides insights into techniques for bypassing rate limits, specifically in the context of the PortSwigger Web Academy.
The second video demonstrates methods for circumventing rate limiting, offering practical advice for security professionals.