How does SafeSEH work?

How does SafeSEH work?

SafeSEH works by instructing the operating system to first check the handler pointers for validity (against a table of known valid EHs) before jumping to them.

What is SEH Windows?

Structured exception handling (SEH) is a Microsoft extension to C to handle certain exceptional code situations, such as hardware faults, gracefully. Although Windows and Microsoft C++ support SEH, we recommend that you use ISO-standard C++ exception handling. It makes your code more portable and flexible.

What is safe SEH?

When /SAFESEH is specified, the linker will only produce an image if it can also produce a table of the image’s safe exception handlers. This table specifies for the operating system which exception handlers are valid for the image. For example, on x64 and ARM, all exception handlers are noted in the PDATA.

What is SEH buffer overflow?

A buffer overflow is when an application attempts to write more data in a buffer than expected or when an application attempts to write more data in a memory area past a buffer. Here we will be discussing a SEH buffer overflow without any memory protections such as DEP or ASLR.

What is control Flowguard?

Control Flow Guard is a feature that makes it harder for exploits to execute arbitrary code through vulnerabilities such as buffer overflows. When a CFG check fails at runtime, Windows immediately terminates the program, thus breaking any exploit that attempts to indirectly call an invalid address.

What is unstructured error handling?

Unstructured exception handling involves the use of the On Error statement. When an exception is raised in a program, control of the program moves to the argument specified in the On Error statement. You use an On Error statement at the beginning of a set of statements, such as a procedure.

What is egg hunting exploit?

Egg Hunters are commonly utilized in situations where there is very limited usable memory available to the exploit author. In short, Egg Hunters allow for a very small amount of shell code to be used to find a much larger piece of shell code somewhere else in memory.

Do flow guards need control?

Control Flow Guard helps prevent memory corruption, which is very helpful to prevent ransomware attacks. The capabilities of the server are restricted to whatever is needed at that point of time to reduce the attack surface.

How does CFG work?

CFG operates by creating a per-process bitmap, where a set bit indicates that the address is a valid destination. Before performing each indirect function call, the application checks if the destination address is in the bitmap. If the destination address is not in the bitmap, the program terminates.

How does SafeSEH work in the operating system?

SafeSEH works by instructing the operating system to first check the handler pointers for validity (against a table of known valid EHs) before jumping to them.

When to use SafeSEH ( image has Safe Exception handlers )?

/SAFESEH[:NO] When /SAFESEH is specified, the linker will only produce an image if it can also produce a table of the image’s safe exception handlers. This table specifies for the operating system which exception handlers are valid for the image.

What happens if / SafeSEH is no in linker?

If /SAFESEH:NO is specified, the linker will not produce an image with a table of safe exceptions handlers even if all modules are compatible with the safe exception handling feature.

How does kiuserexceptiondispatcher in Windows SafeSEH work?

When an exception hits, ntdll.dll!KiUserExceptionDispatcher will try to figure out which exception in the SEH chain to use. In turn, each exception handler address is scanned for in this list (by ntdll.dll). If it is found, then the exception filter is allowed to run.