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.




Related word

1. Hacking Tools Mac
2. Hacker Tools For Mac
3. Termux Hacking Tools 2019
4. Hacking Tools For Windows
5. Hak5 Tools
6. Hacker Tools Software
7. Pentest Tools Framework
8. How To Hack
9. Best Pentesting Tools 2018
10. Best Pentesting Tools 2018
11. What Is Hacking Tools
12. Hacker Tools Mac
13. Usb Pentest Tools
14. Computer Hacker
15. Hacking Tools For Windows Free Download
16. Hacker Tool Kit
17. Hacking Tools Kit
18. Pentest Recon Tools
19. Hacking Tools Pc
20. Hacking Tools Windows
21. What Is Hacking Tools
22. Hack Tools For Mac
23. Hacking Tools For Windows 7
24. Hacks And Tools
25. Pentest Recon Tools
26. Pentest Tools Kali Linux
27. Hacker Tools 2020
28. Pentest Tools List
29. Hack And Tools
30. Hack Tools
31. Hacking Tools Hardware
32. Hack App
33. Hacker Tools Free Download
34. Hacker Tools For Windows
35. What Are Hacking Tools
36. Pentest Tools Alternative
37. Nsa Hack Tools Download
38. Hacker Tools Apk
39. Hacking Tools Windows 10
40. Install Pentest Tools Ubuntu
41. Pentest Tools Tcp Port Scanner
42. Hacker Tools For Windows
43. Pentest Tools Bluekeep
44. Pentest Tools For Windows
45. Hacker Tool Kit
46. Hacker Tools
47. Hacking Tools And Software
48. Bluetooth Hacking Tools Kali
49. Pentest Tools Url Fuzzer
50. Hack Tools Pc
51. Hack Tool Apk No Root
52. Beginner Hacker Tools
53. Hacking Tools Name
54. Pentest Tools Kali Linux
55. Hacking Tools Software
56. Pentest Tools Find Subdomains
57. Hack Tools For Ubuntu
58. Pentest Tools Framework
59. Hacker Tools Github
60. Hacking Tools For Kali Linux
61. Hack Tools
62. Pentest Tools Alternative
63. Hack Rom Tools
64. Termux Hacking Tools 2019
65. Hacking App
66. Pentest Reporting Tools
67. Hacker Tool Kit
68. World No 1 Hacker Software
69. Hackrf Tools
70. Pentest Tools Port Scanner
71. Usb Pentest Tools
72. Hacker Tools Apk Download
73. Hacking Tools Windows 10
74. Pentest Tools Review
75. Best Hacking Tools 2020
76. Nsa Hack Tools Download
77. Pentest Tools Bluekeep
78. How To Install Pentest Tools In Ubuntu
79. Pentest Tools Free