Debug dos program

The Debug programs user right can be exploited to capture sensitive device information from system memory or to access and modify kernel or application structures. Some attack tools exploit this user right to extract hashed passwords and other private security information or to insert malware.

By default, the Debug programs user right is assigned only to administrators, which helps mitigate risk from this vulnerability. Remove the accounts of all users and groups that do not require the Debug programs user right. If you revoke this user right, no one can debug programs. However, typical circumstances rarely require this capability on production devices. If an issue arises that requires an application to be debugged on a production server, you can move the server to a different organizational unit OU temporarily and assign the Debug programs user right to a separate Group Policy for that OU.

Skip to main content. This browser is no longer supported. Up to 10, optional breakpoint addresses may be set by simply listing them on the '-g' command line; separated by spaces. DEBUG will halt execution just before any of breakpoint addresses is about to be executed, and all of them will be 'cleared' at this time as well.

Using " Go " after setting breakpoints at instructions you're sure DEBUG understands is one way you can get more use out of this program; for example, when debugging the "real" code of a Master Boot Record written for an or above processor. DEBUG won't be able to disassemble, nor step through, such code, but it can pass the code for those type of instructions to the CPU for immediate execution , and still stop at the breakpoint s you've set for any instruction that it does understand!

The instructions at these locations are restored to their original bytes ONLY if one of the breakpoints is encountered.

So, don't ever save the code unless you're sure all breakpoints have been cleared! Saving your work to a backup copy before ever using a breakpoint is the best way to avoid corrupting the code.

Technical Notes: The "User" stack pointer must be valid and have 6 bytes available for this command to function correctly. An iret instruction is used to jump to the first breakpoint encountered. So if the User Stack is not valid or is too small, the operation might crash. The 'A' command remembers the last location where any data was assembled, so successive 'A' commands when no address is specified will always begin at the next address in the chain of assembled instructions.

This aspect of the command is similar to the Dump command which remembers the location of its last dump if no new address is specified. Example s:. Using the character string from our E Enter command above:. ENTER the characters in bold blue type ; you do not need to enter the comments after the semi-colon ; symbols:.

For example, you can copy and paste the following into DEBUG after entering an initial "a" command and obtain the same results as above:. This is especially true when trying to directly access hard disks! Under real DOS, they can still be used for direct communications with keyboards or a floppy drive's control chips along with many other hardware devices.

Here's an example of how to read the hours and minutes from a computer's "real time clock" RTC :. See comments under the Input command. Once again, this shows how limited DEBUG is compared to any utility that can view the raw data on either a hard drive or diskette. Unlike hard disks, the very first sector on a floppy disk is an OS Boot sector.

Here's what you might see from a Logical disk sector and some d umps from a couple floppy disks. However, if you keep a binary copy of a good floppy disk Boot Sector somewhere, you could use DEBUG to overwrite whatever's on a faulty floppy disk's first sector see Write command. But if you really need to see what's in such a Boot sector i.

It might simply have been formatted with a file system it cannot recognize such as Linux's ext2 and could easily boot-up on its own; a very good reason for labeling your disks!

What kind of OEM Name is that? Someone at Microsoft decided that this was where they'd place a new pseudo-random type of identification to make sure that any information cached by ' Windows 9x ' from one disk wouldn't be mixed up with info from a different one if you swapped disks. The whole string begins with five pseudo-random hex bytes , and always ends with the characters IHC.

Once Windows has written this string, it will remain the same for any future disk reads or writes. DEBUG's code went through a number of changes and 'bug fixes' too over the years! Some of these internal changes were related to DOS system calls and screen output, then there was the change in file type from a. COM to an. But in spite of all those changes and others which followed, DEBUG has never had an official revision since 2. Though it seems a great deal has changed, you'll still find the phrase "Vers 2.

But without access to its source code, we can't be sure if there were any major differences in DEBUG. So, one has to wonder what the cause of this problem might be. See the L command in the Tutorial section for more information. This may surprise you: We purposely mentioned the DOS 5. No doubt he wished it had been replaced by something better way back in It wasn't until the release of DOS 5. COM program v 1. DEBUG can also be quite useful for educational purposes.

And even for debugging the Assembly code that is required during the boot process: The software that checks the Partition Table on hard disks and loads OS Boot Sectors into Memory. SEE our Bochs Debug page for more on that. You can download and use this program for free; currently we recommend a page made for it on a site created by Vernon C.

Unfortunately, as with DEBUG itself, this program will not function under any bit Windows OS; attempting to do so will result in this error message:. DEBUG was originally designed to work with. COM programs having a maximum size of only 65, bytes [ 64 x - ] or less ; how much less, depended upon the maximum number of bytes the program had to place on the Stack at the same time. The subtraction of bytes is necessary since DEBUG often uses the area from offset 00 through FF hex for some internal data such as the name of the file that was loaded.

Remember, true. As early as DOS 1. Basically, how large a file that DEBUG can safely use without error depends on the amount of available memory and the way the OS handles memory management. We'll say more about this below. EXE , it: 1 Allocates at least 64 KiB of the first free Memory Segment for debugging programs or examining files specified on the command line. Just how large a file it can handle, depends upon both the OS and available memory.

And remember that j ust because your system can debug a certain file, doesn't mean someone else's will be able to. But due to the automatic h load offset, the file's last bytes will have been loaded at the beginning of the next 64 KiB segment.