Linux Stack Protection By Default

Modern gcc compiler (v9.2.0) protects the stack by default and you will notice it because instead of SIGSEGV on stack overflow you will get a SIGABRT, but it also generates coredumps.

In this case the compiler adds the variable local_10. This variable helds a canary value that is checked at the end of the function.
The memset overflows the four bytes stack variable and modifies the canary value.

The 64bits canary 0x5429851ebaf95800 can't be predicted, but in specific situations is not re-generated and can be bruteforced or in other situations can be leaked from memory for example using a format string vulnerability or an arbitrary read wihout overflowing the stack.

If the canary doesn't match, the libc function __stack_chck_fail is called and terminates the prorgam with a SIGABORT which generates a coredump, in the case of archlinux managed by systemd and are stored on "/var/lib/systemd/coredump/"


❯❯❯ ./test 
*** stack smashing detected ***: terminated
fish: './test' terminated by signal SIGABRT (Abort)

❯❯❯ sudo lz4 -d core.test.1000.c611b7caa58a4fa3bcf403e6eac95bb0.1121.1574354610000000.lz4
[sudo] password for xxxx: 
Decoding file core.test.1000.c611b7caa58a4fa3bcf403e6eac95bb0.1121.1574354610000000 
core.test.1000.c611b : decoded 249856 bytes 

 ❯❯❯ sudo gdb /home/xxxx/test core.test.1000.c611b7caa58a4fa3bcf403e6eac95bb0.1121.1574354610000000 -q 

We specify the binary and the core file as a gdb parameters. We can see only one LWP (light weight process) or linux thread, so in this case is quicker to check. First of all lets see the back trace, because in this case the execution don't terminate in the segfaulted return.

We can see on frame 5 the address were it would had returned to main if it wouldn't aborted.

Happy Idea: we can use this stack canary aborts to detect stack overflows. In Debian with prevous versions it will be exploitable depending on the compilation flags used.
And note that the canary is located as the last variable in the stack so the previous variables can be overwritten without problems.




Continue reading

1. Pentest Tools Github
2. How To Install Pentest Tools In Ubuntu
3. Best Hacking Tools 2019
4. Hacking Tools 2019
5. Hacking Tools Free Download
6. Hacker Tools For Ios
7. Hack Tools Github
8. Hack Tools Online
9. Hacker Tool Kit
10. Hacking Tools For Mac
11. Pentest Tools Kali Linux
12. How To Install Pentest Tools In Ubuntu
13. Hack Tools Download
14. How To Install Pentest Tools In Ubuntu
15. Hack Tools Online
16. Hacking Tools For Beginners
17. New Hack Tools
18. How To Hack
19. Hacker Tools For Mac
20. Nsa Hack Tools
21. Pentest Tools Github
22. Hackrf Tools
23. Best Hacking Tools 2020
24. Hacker Tools Free Download
25. Pentest Tools Linux
26. Pentest Tools For Mac
27. Pentest Box Tools Download
28. Android Hack Tools Github
29. Hacking Tools For Windows Free Download
30. Pentest Tools Website
31. Hack Tools For Mac
32. Pentest Tools List
33. Hacker Tools
34. Hacker Tools Windows
35. Pentest Tools Linux
36. Hack Tools For Games
37. Pentest Tools Bluekeep
38. Hacker Hardware Tools
39. Hacking Tools Windows 10
40. What Are Hacking Tools
41. Pentest Tools Open Source
42. Best Pentesting Tools 2018
43. Hacking Tools For Windows 7
44. Pentest Tools
45. Pentest Tools Website Vulnerability
46. Hacking Tools Windows 10
47. Pentest Tools Website Vulnerability
48. Hacking Tools For Windows 7
49. Pentest Tools Port Scanner
50. Hacking Tools 2019
51. Hacker Tools Apk Download
52. Blackhat Hacker Tools
53. Hack Tools Download