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 articles

1. Hackers Toolbox
2. Hacking Tools For Windows
3. Hack Tools
4. Pentest Tools Framework
5. Tools For Hacker
6. Pentest Tools List
7. Hacker Tools List
8. Hacking Tools For Windows 7
9. Hacking Tools Mac
10. Hacker Tools List
11. Hackers Toolbox
12. Hacker Tools Apk Download
13. Pentest Tools Online
14. Hack Tools For Windows
15. Hacking Tools For Windows
16. Hacker Tools Apk
17. Best Hacking Tools 2019
18. Hack Tools For Games
19. What Is Hacking Tools
20. Pentest Recon Tools
21. Pentest Tools
22. Hacking Tools Kit
23. Hack App
24. Pentest Tools Github
25. Hacker Tools Free
26. New Hacker Tools
27. Hacking Tools Mac
28. Hack Tools Online
29. Usb Pentest Tools
30. Hacker Tools Github
31. Hacker Tools
32. New Hacker Tools
33. Hack Tools Online
34. Hack Tools For Pc
35. Pentest Tools For Android
36. Pentest Tools
37. Pentest Tools Alternative
38. Black Hat Hacker Tools
39. Best Pentesting Tools 2018
40. Hacking Tools Software
41. Kik Hack Tools
42. Hacking Tools 2019
43. Growth Hacker Tools
44. Hacker Tools For Pc
45. Hacking Tools For Beginners
46. How To Hack
47. Usb Pentest Tools
48. Tools 4 Hack
49. Pentest Tools Review
50. Hacking Tools For Beginners
51. Hacking Tools 2019
52. Hacking Tools Software
53. Ethical Hacker Tools
54. Hacking Tools Online
55. Pentest Tools For Windows
56. Hacker Tools Apk Download
57. New Hacker Tools
58. Hacker Tools List
59. New Hack Tools
60. Computer Hacker
61. Bluetooth Hacking Tools Kali
62. Hacking Tools Windows
63. Hacking Tools For Windows 7
64. Pentest Recon Tools
65. Hacker Tool Kit
66. Hacking Tools Hardware
67. Beginner Hacker Tools
68. Pentest Tools Website
69. Hacking Tools For Kali Linux
70. Hacker Tool Kit
71. Pentest Recon Tools
72. Pentest Tools Port Scanner
73. What Is Hacking Tools
74. Pentest Tools Nmap
75. Hack Tools
76. Install Pentest Tools Ubuntu
77. Black Hat Hacker Tools
78. Hacker Techniques Tools And Incident Handling
79. Pentest Tools Alternative
80. Game Hacking
81. Pentest Tools Windows
82. Pentest Tools Download
83. New Hacker Tools
84. Hacking Tools For Mac
85. Top Pentest Tools
86. Best Hacking Tools 2019
87. Physical Pentest Tools
88. Beginner Hacker Tools
89. Tools For Hacker
90. New Hacker Tools
91. Nsa Hack Tools
92. Pentest Tools Url Fuzzer
93. Pentest Tools Free
94. Android Hack Tools Github
95. Hacks And Tools
96. Nsa Hack Tools
97. Termux Hacking Tools 2019
98. Ethical Hacker Tools
99. Hacker Search Tools
100. Free Pentest Tools For Windows
101. Hacking Tools
102. Game Hacking
103. Hacking Tools Windows
104. Termux Hacking Tools 2019
105. Nsa Hack Tools Download
106. Best Hacking Tools 2019
107. Hacker Tools Mac
108. Pentest Tools Linux
109. Nsa Hack Tools
110. Hacker Hardware Tools
111. Hacker Tools Linux
112. Hack Tools For Windows
113. Pentest Tools Tcp Port Scanner