Here are several strategies to defend against SMS bombing (SMS flood attacks):
Rate Limiting: Implement strict rate limits on SMS sending per phone number or IP address within a specific time window. For example, allow only 5 SMS requests per minute per phone number.
CAPTCHA Verification: Require users to complete a CAPTCHA challenge before sending SMS requests. This helps block automated bots.
Phone Number Whitelisting/Blacklisting: Restrict SMS services to trusted phone numbers (whitelisting) or block known malicious numbers (blacklisting).
Behavioral Analysis: Monitor user behavior patterns, such as sudden spikes in SMS requests, and flag or block suspicious activity.
Two-Factor Authentication (2FA) Alternatives: Offer alternative 2FA methods like app-based authenticators (e.g., Tencent Cloud SMS Verification with multi-factor options) to reduce reliance on SMS.
SMS Gateway Protection: Use secure SMS gateways with built-in anti-fraud mechanisms, such as Tencent Cloud SMS, which provides fraud detection and request filtering.
User Reporting & Feedback: Allow users to report spam or suspicious SMS messages, enabling quick action against abusive accounts.
API Authentication: Secure SMS APIs with token-based authentication (e.g., OAuth 2.0) to prevent unauthorized access.
For example, if a banking app detects 100 SMS requests from a single IP in 1 minute, it can temporarily block further requests and require CAPTCHA verification. Tencent Cloud SMS services include anti-fraud features and rate-limiting tools to help mitigate such attacks.