OTP Bypass Vulnerability Through Swapping

You Should Know:

The OTP bypass vulnerability through swapping is a critical security flaw that can be exploited by attackers to gain unauthorized access to user accounts. Here’s a detailed breakdown of how this vulnerability works and how you can test and mitigate it in your systems.

How the Bug Works:

1. OTP Format and Time Constraint: The OTP format is typically alphanumeric (e.g., ‘G8GK90’), making brute-forcing impractical. Additionally, the OTP is valid for only 3 minutes.
2. Swapping OTPs: An attacker creates two accounts simultaneously—[email protected] (user1) and `[email protected]` (user2). Both accounts receive OTPs, but the attacker uses the OTP from `[email protected]` to verify [email protected]. The system accepts any valid OTP, even if it belongs to a different email.

Steps to Reproduce:

1. Create Two Accounts: Use two different email addresses to create accounts on the target system.
2. Capture OTPs: Ensure both accounts receive their respective OTPs.
3. Swap OTPs: Use the OTP from the first account to verify the second account.
4. Verify Exploit: If the second account is successfully verified, the vulnerability exists.

Mitigation Steps:

1. Bind OTP to Email: Ensure that the OTP is strictly bound to the email address it was sent to. The system should reject OTPs that do not match the email address.
2. Implement Rate Limiting: Limit the number of OTP attempts per account to prevent brute-forcing.
3. Use Multi-Factor Authentication (MFA): Combine OTP with other authentication factors like biometrics or hardware tokens.
4. Audit OTP Implementation: Regularly review and test the OTP implementation for vulnerabilities.

Practice Verified Commands and Codes:

Linux Command to Simulate OTP Binding:

<h1>Simulate OTP binding to email</h1>

if [ "$OTP" == "$STORED_OTP" ] && [ "$EMAIL" == "$STORED_EMAIL" ]; then
echo "OTP Verified Successfully"
else
echo "OTP Verification Failed"
fi

Python Script to Test OTP Binding:

def verify_otp(email, otp, stored_email, stored_otp):
if otp == stored_otp and email == stored_email:
return "OTP Verified Successfully"
else:
return "OTP Verification Failed"

<h1>Example Usage</h1>

email = "[email protected]"
otp = "G8GK90"
stored_email = "[email protected]"
stored_otp = "G8GK90"

print(verify_otp(email, otp, stored_email, stored_otp))

Windows PowerShell Script for OTP Validation:

<h1>PowerShell script to validate OTP</h1>

$email = "[email protected]"
$otp = "G8GK90"
$stored_email = "[email protected]"
$stored_otp = "G8GK90"

if ($otp -eq $stored_otp -and $email -eq $stored_email) {
Write-Output "OTP Verified Successfully"
} else {
Write-Output "OTP Verification Failed"
}

What Undercode Say:

The OTP bypass vulnerability through swapping is a serious security issue that can lead to unauthorized account access. It is crucial to bind OTPs to the specific email addresses they are sent to and implement additional security measures like rate limiting and multi-factor authentication. Regular security audits and penetration testing can help identify and mitigate such vulnerabilities before they are exploited.

For further reading on secure OTP implementation, refer to OWASP Authentication Cheat Sheet.

References:

Reported By: Subrati Swaroop – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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