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Fatal exception

Fatal exception definition

A fatal exception is an error in a computer program or system that prevents it from continuing to operate correctly. When encountered, the system usually crashes, often providing an error message to inform the user about the nature of the problem.

How a fatal exception works

When software operates, it follows specific rules and paths known as code. If something unexpected occurs outside of what the code can handle, a fatal exception can arise. This means the software encounters a situation it wasn't programmed to deal with and doesn't know how to proceed. As a result, the program usually stops or crashes to prevent potential data corruption or further issues.

Fatal exception examples

  • Division by zero. In many programming environments, trying to divide a number by zero results in a fatal exception since it's mathematically undefined.
  • Memory access violation. If software tries to access a memory location not allocated to it or attempts to write to a read-only location, it can throw a fatal exception.
  • Stack overflow. If a program uses more stack (a type of memory) than what's available, typically due to infinite recursion, it can lead to a fatal exception.
  • Invalid code execution. A fatal exception can occur if a program tries to execute data that isn’t valid instructions.
  • Resource unavailability. If a program tries to access a necessary resource (like a file or network connection) that's unavailable, it might encounter a fatal exception, especially if it's not programmed to handle such scenarios.

Security considerations of fatal exceptions

  • Information disclosure. When a program crashes due to a fatal exception, its error message or crash dump might disclose sensitive information about the system, application configuration, or even user data. Attackers can use this information to fine-tune their subsequent attacks.
  • Denial of service (DoS). If a malicious actor knows what triggers a fatal exception in a software system, they can induce it over and over. This will cause the system to crash multiple times, denying legitimate users access to the service.
  • Buffer overflows. One of the most well-known ways to exploit a program is through buffer overflow attacks. By inputting more data than a buffer can handle (typically due to lack of bounds checking), an attacker can cause the program to throw a fatal exception. More critically, they can overwrite critical memory sections, leading to arbitrary code execution.
  • Bypassing security mechanisms. Some security mechanisms might be bypassed if a fatal exception occurs. For example, if a security check causes an exception, and the system's reaction is to skip the check and continue, it could leave a door open for further exploitation.
  • Chaining exploits. In some scenarios, a fatal exception might be part of a multi-step process. An attacker could induce an exception as a precursor to another vulnerability they wish to exploit.