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.




Read more

1. Best Hacking Tools 2020
2. Hacker Tools For Pc
3. Hacking Tools Online
4. Hack App
5. Hacker Tools For Pc
6. Hacking Tools For Beginners
7. Hacker Techniques Tools And Incident Handling
8. Hack Apps
9. Hacker Tools Software
10. Hacking Tools Pc
11. Hacker Tools 2019
12. Hacker Techniques Tools And Incident Handling
13. Pentest Tools For Mac
14. Pentest Tools Framework
15. Growth Hacker Tools
16. Black Hat Hacker Tools
17. Hacker Tools Windows
18. Hacker
19. Hack Tools For Mac
20. Best Pentesting Tools 2018
21. Hack Tools For Pc
22. How To Make Hacking Tools
23. Hacking App
24. What Are Hacking Tools
25. Nsa Hacker Tools
26. Pentest Tools Windows
27. Hacker Search Tools
28. Hackers Toolbox
29. Hak5 Tools
30. Hacking Tools Windows
31. Hacking Tools Online
32. Game Hacking
33. Hacking App
34. Hacker Tools Software
35. Pentest Tools Port Scanner
36. Pentest Tools Download
37. Hack And Tools
38. Hack App
39. Pentest Tools
40. Hacker Tools Free Download
41. Beginner Hacker Tools
42. Hacker Tools
43. Hacking Tools For Windows
44. Hacking Tools Windows
45. Hacking Tools Pc
46. How To Make Hacking Tools
47. Hacker Tools Free
48. Hacker Tools List
49. Hacker Tools Apk Download
50. Pentest Tools Download
51. Game Hacking
52. Android Hack Tools Github
53. Hacker Tools Online
54. Hack Tools Online
55. Hacking Tools Usb
56. What Is Hacking Tools
57. Hacking Tools
58. Hacking App
59. Hacking Tools Usb
60. Hack Tools For Windows
61. Beginner Hacker Tools
62. Hacker Tools Online
63. Pentest Tools
64. Free Pentest Tools For Windows
65. Game Hacking
66. Hacker Tools For Windows
67. Pentest Tools For Mac
68. Hacking Tools Software
69. Best Hacking Tools 2020
70. Pentest Automation Tools
71. What Are Hacking Tools
72. Hacker Search Tools
73. Underground Hacker Sites
74. Hack Website Online Tool
75. Github Hacking Tools
76. Termux Hacking Tools 2019
77. Hack Website Online Tool
78. Hacking Tools For Windows Free Download
79. New Hacker Tools
80. Hack Apps
81. Hacker Tools Apk Download
82. Hack Tools Mac
83. Best Pentesting Tools 2018
84. Top Pentest Tools
85. Pentest Tools For Windows
86. Pentest Tools Review
87. Termux Hacking Tools 2019
88. Pentest Tools Website
89. Pentest Automation Tools
90. Pentest Tools Subdomain
91. Hacking Tools Usb
92. Nsa Hack Tools Download
93. Hacker Tools
94. Hacker Search Tools
95. What Is Hacking Tools
96. Top Pentest Tools
97. World No 1 Hacker Software
98. Nsa Hacker Tools
99. Hacking App
100. Pentest Tools For Android
101. Hacker Tools 2020
102. Pentest Tools Tcp Port Scanner
103. Hacker Tools For Windows
104. Hack Tools
105. Pentest Tools Find Subdomains
106. What Is Hacking Tools
107. Pentest Tools Apk
108. Hack Tool Apk No Root
109. Hacking Apps
110. Hacking Tools Online
111. Hacker Tools List
112. Pentest Tools List
113. Hacker Tools For Ios
114. Hacker Tools For Mac
115. Top Pentest Tools
116. Hak5 Tools
117. Kik Hack Tools
118. Pentest Tools Alternative
119. Hack Tools For Mac
120. Computer Hacker
121. Nsa Hacker Tools
122. Pentest Tools Alternative
123. Hacking Tools Download
124. Pentest Tools For Android
125. Pentest Tools Nmap
126. Pentest Tools Website Vulnerability
127. Hacking Tools For Games
128. Hackers Toolbox