Dangerous Signal Handler not Disabled During Sensitive Operations

Signal handlers in a program often run with elevated privileges and manage critical data. If a handler is written to share state—like global variables or file descriptors—with other handlers, and the program doesn't temporarily disable (or 'mask') incoming signals, a major risk emerges. An attacker can exploit this by sending a second signal while the first handler is still executing, triggering a different handler that modifies the same shared resources. This uncontrolled interruption corrupts the program's internal state because the first handler's assumptions about that state become invalid. The result is often a crash, data loss, or undefined behavior that an attacker can potentially leverage to gain control of the application or cause a denial of service. To prevent this, developers must design signal handlers to either be re-entrant (stateless) or ensure all related signals are masked for the handler's entire duration.