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.




More information

1. Hack Tools Pc
2. How To Install Pentest Tools In Ubuntu
3. Computer Hacker
4. Wifi Hacker Tools For Windows
5. Pentest Tools For Ubuntu
6. Hacking Tools Pc
7. Hacker
8. Hack Tools For Mac
9. Hacking Tools For Kali Linux
10. Hacker Tools For Ios
11. Hacking Tools For Windows 7
12. Pentest Tools Open Source
13. Pentest Tools Port Scanner
14. Hacking Tools And Software
15. Pentest Tools Alternative
16. Hacker Tools 2020
17. Hacker Tools For Pc
18. What Is Hacking Tools
19. Hacking Tools Github
20. Pentest Tools For Mac
21. What Are Hacking Tools
22. Pentest Tools Port Scanner
23. Hacking Tools
24. Hack Tools
25. Hacker Tools
26. Hacker Security Tools
27. Hacking Tools Windows
28. Hacker Tools For Mac
29. Hack Tools Online
30. Pentest Tools Open Source
31. Top Pentest Tools
32. Hacking Tools Online
33. Pentest Tools Windows
34. Hacking Tools Software
35. Hacker Tools Free Download
36. Pentest Tools Alternative
37. Hacker Tools Software
38. Pentest Tools Linux
39. Best Pentesting Tools 2018
40. Blackhat Hacker Tools
41. Pentest Recon Tools
42. Hacker Tools Github
43. Hacking Tools For Kali Linux
44. Pentest Tools Framework
45. Hacking Tools And Software
46. Pentest Tools
47. Hack App
48. Install Pentest Tools Ubuntu
49. Pentest Tools Free
50. Pentest Reporting Tools
51. Computer Hacker
52. Hacker Tools
53. Pentest Tools Tcp Port Scanner
54. Free Pentest Tools For Windows
55. Hacking Tools For Mac
56. Hack Tools
57. Pentest Reporting Tools
58. Pentest Tools Nmap
59. Hacker Tools Windows
60. Hack Tools Online
61. Hacker Tools For Mac
62. Pentest Recon Tools
63. Pentest Tools Review
64. Hacking Tools Kit
65. Hackers Toolbox
66. Hacker Tools List
67. Hacking App
68. Pentest Tools List
69. Nsa Hack Tools
70. Tools Used For Hacking