Race Condition ve TOCTOU Exploit'leri: Concurrency Vulnerabilities

Race condition ve Time-of-Check to Time-of-Use (TOCTOU) exploit'leri, concurrent execution timing discrepancy'lerinden yararlanan vulnerability class'ıdır ve web application, OS ve file system'lerde bulunur. TOCTOU vulnerability, check operation (permission validation, existence check) ve use operation (file access, resource usage) arasında time gap exploitation ile privilege escalation veya unauthorized access sağlar; file symlink race ve atomic operation bypass yaygın vektörlerdir. HTTP request race condition, concurrent HTTP request'ler ile state inconsistency exploitation yapılır; promo code double-use, password reset token reuse ve payment race condition örnekleridir ve HTTP/2 multiplexing ile exploitation kolaylaşır. Symlink race attack, file creation ve permission check arasında symlink creation ile arbitrary file overwrite veya read yapılır; /tmp directory race condition ve world-writable directory exploitation yaygındır ve safe file creation API'leri ile mitigation sağlanır. Race condition detection, static analysis ile concurrent access pattern identification, dynamic testing ile thread interleaving exploration ve fuzzing ile race trigger discovery yapılır; ThreadSanitizer ve Helgrind race detection araçlarıdır. Mitigation, atomic operations, mutex/lock synchronization, immutable data structures ve transaction isolation ile race condition prevention sağlanır; defensive programming ve concurrent code review best practices'tir.