Learn and Earn with the Most Common Unsecured Methods of OTP Bypass Techniques: Unpacking the Pitfalls

Discover the ultimate guide for bug bounty hunters to detect sneaky OTP validation vulnerabilities!

4 min readJul 11, 2023



As the digital world expands, so does the importance of cybersecurity. One Time Passwords (OTP) have become increasingly popular in the realm of authentication. They are known for providing an extra layer of security, making it difficult for hackers to gain unauthorized access. However, if not properly implemented, OTP validation can leave a system open to various security risks. Let’s explore six of the most common unsecured methods of OTP validation.

1. OTP Leakage in Response

When the application back-end system generates an OTP, it’s crucial that this information remains confidential. One common insecure practice is when the OTP leaks through server responses. This can happen when the OTP, once generated, is included in HTTP responses, logs, or error messages that can be intercepted by attackers. Ensuring OTPs are kept hidden in responses is key to maintaining their integrity and confidentiality.

OTP is disclosed in Response

2. Weak OTP Length

The length and complexity of an OTP significantly impact its security. A short OTP 4 & 5 digit or one without a mixture of characters, numbers, and symbols can easily be cracked by brute force attacks. As a rule of thumb, OTPs should be of sufficient length (at least six characters) and complexity, involving a mix of alphanumeric and special characters.

3. Insecure OTP Validation logic on the server side.

In an ideal scenario, once a user enters the OTP, the system checks it on the server side for validation and only then grants access to certain actions or information. However, when this process is misconfigured, it can lead to substantial security vulnerabilities. A significant misstep is when the OTP state is insecurely validated on the server side.