What is fs:0x28 in x86 assembly?

by | May 31, 2022 | Featured, Reverse Engineering

fs:0x28 In x86 Assembly
  400570:	mov    rdx,QWORD PTR [rbp-0x8]
  400574:	xor    rdx,QWORD PTR fs:0x28
  40057b:	00 00 
  40057d:	je     400584 <main+0x3e>
  40057f:	call   400420 <__stack_chk_fail@plt>

The stack canary is stored in [RBP – 0x8]. So, this value is moved to RDX. Then, we are checking whether the stored value is unchanged and is equal to fs:0x28. If the value changes, we call __stack_chk_fail@plt which notifies the stack frame is corrupted.

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Amrita Mitra

Author

Ms. Amrita Mitra is an author, who has authored the books “Cryptography And Public Key Infrastructure“, “Web Application Vulnerabilities And Prevention“, “A Guide To Cyber Security” and “Phishing: Detection, Analysis And Prevention“. She is also the founder of Asigosec Technologies, the company that owns The Security Buddy.

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