OpenSSL TOTP Rate Limiter Bypass in Encryption

Executive Summary

This vulnerability affects openssl_encrypt versions before 1.4.0. It involves a TOTP brute-force rate limiter that uses an in-memory system not shared across server workers. Each worker has its own rate limit state, and the state resets when the server restarts. Attackers can bypass rate limits by distributing attempts across multiple servers or retrying immediately after a restart.

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Detection Guidance

Check if your openssl_encrypt version is below 1.4.0 by running: openssl_encrypt --version. If vulnerable, inspect server logs for repeated failed TOTP attempts across workers or after restarts. Monitor authentication failures that bypass rate limits.

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Impact Analysis

Attackers can bypass authentication protections by distributing brute-force attempts across multiple server instances or retrying right after a server restart. This increases the risk of unauthorized access to systems relying on TOTP for security. The vulnerability is particularly dangerous in multi-worker or distributed server environments.

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Compliance Impact

This vulnerability could impact compliance with GDPR and HIPAA by failing to enforce adequate brute-force protection for TOTP authentication. GDPR requires appropriate security measures to protect personal data, while HIPAA mandates safeguards against unauthorized access. The lack of shared rate limiting across workers and server restarts may allow attackers to bypass authentication, potentially leading to unauthorized data access or breaches.

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Mitigation Strategies

Upgrade openssl_encrypt to version 1.4.0 or later. If upgrading isn't possible, configure a shared rate limiter like Redis or a database. Ensure rate limit state persists across server restarts to prevent immediate retries.

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