Link to this headingGDB
https://github.com/al13n321/nnd debugger
Link to this headingReading Values from Memory
Read 32 bits:
gdb$ x/64wx 0x606000
0x606000 <path.4275+3360>: 0x00000000 0x00000000 0x00000000 0x00000000
0x606010 <path.4275+3376>: 0x00000000 0x00000000 0x00000000 0x00000000
0x606020 <path.4275+3392>: 0x00000000 0x00000000 0x00000000 0x00000000
0x606030 <path.4275+3408>: 0x00000000 0x00000000 0x00000000 0x00000000
0x606040 <path.4275+3424>: 0x00000000 0x00000000 0x00000000 0x00000000
0x606050 <path.4275+3440>: 0x00000000 0x00000000 0x00000000 0x00000000
0x606060 <path.4275+3456>: 0x00000000 0x00000000 0x00000000 0x00000000
0x606070 <path.4275+3472>: 0x00000000 0x00000000 0x00000000 0x00000000
0x606080 <path.4275+3488>: 0x00000000 0x00000000 0x00000000 0x00000000
0x606090 <path.4275+3504>: 0x00000000 0x00000000 0x00000000 0x00000000
0x6060a0 <path.4275+3520>: 0x00000000 0x00000000 0x00000000 0x00000000
0x6060b0 <path.4275+3536>: 0x00000000 0x00000000 0x00000000 0x00000000
0x6060c0 <path.4275+3552>: 0x00000000 0x00000000 0x00000000 0x00000000
0x6060d0 <path.4275+3568>: 0x00000000 0x00000000 0x00000000 0x00000000
0x6060e0 <path.4275+3584>: 0x00000000 0x00000000 0x00000000 0x00000000
0x6060f0 <path.4275+3600>: 0x00000000 0x00000000 0x00000000 0x00000000
Read 64 bits:
gef➤ x/20gx $rsp-0x8
0x7ffd6864d4d8: 0x0000000000401062 0x0000000000401001
0x7ffd6864d4e8: 0x00007ffd6864f1c7 0x00007ffd6864f1e4
0x7ffd6864d4f8: 0x0000000000000000 0x00007ffd6864f1ec
0x7ffd6864d508: 0x00007ffd6864f220 0x00007ffd6864f238
0x7ffd6864d518: 0x00007ffd6864f24b 0x00007ffd6864f264
0x7ffd6864d528: 0x00007ffd6864f26c 0x00007ffd6864f27c
0x7ffd6864d538: 0x00007ffd6864f299 0x00007ffd6864f2b0
0x7ffd6864d548: 0x00007ffd6864f2d6 0x00007ffd6864f2e5
0x7ffd6864d558: 0x00007ffd6864f2f9 0x00007ffd6864f304
0x7ffd6864d568: 0x00007ffd6864f33e 0x00007ffd6864f367
Read Strings from the stack:
gef➤ x/5s $rsp -0x8
0x7fffffffde38: "8Af9Ag0Ag1Ag2Ag3\272\341\377\377\377\177"
0x7fffffffde4f: ""
0x7fffffffde50: ""
0x7fffffffde51: ""
0x7fffffffde52: ""
Link to this headingUseful GEF Commands
For permissions a s means shared memory and a p means private memory.
MAP_SHARED allows any other process that has that same memory mapped to access the data
MAP_PRIVATE does not allow any other process that has the same memory mapped to access the data
View mapped memory segments the heap/stack and the actual program code:
gef➤ vmmap
Start End Offset Perm Path
0x00400000 0x00401000 0x00000000 r-x /home/user/challenges-day1/challenge1
0x00410000 0x00411000 0x00000000 r-x /home/user/challenges-day1/challenge1
0x00411000 0x00412000 0x00001000 rwx /home/user/challenges-day1/challenge1
0xb6ede000 0xb6fc0000 0x00000000 r-x /lib/arm-linux-gnueabihf/libc-2.27.so
0xb6fc0000 0xb6fd0000 0x000e2000 --- /lib/arm-linux-gnueabihf/libc-2.27.so
0xb6fd0000 0xb6fd2000 0x000e2000 r-x /lib/arm-linux-gnueabihf/libc-2.27.so
0xb6fd2000 0xb6fd3000 0x000e4000 rwx /lib/arm-linux-gnueabihf/libc-2.27.so
0xb6fd3000 0xb6fd6000 0x00000000 rwx
0xb6fd6000 0xb6fee000 0x00000000 r-x /lib/arm-linux-gnueabihf/ld-2.27.so
0xb6ff9000 0xb6ffb000 0x00000000 rwx
0xb6ffb000 0xb6ffc000 0x00000000 r-x [sigpage]
0xb6ffc000 0xb6ffd000 0x00000000 r-- [vvar]
0xb6ffd000 0xb6ffe000 0x00000000 r-x [vdso]
0xb6ffe000 0xb6fff000 0x00018000 r-x /lib/arm-linux-gnueabihf/ld-2.27.so
0xb6fff000 0xb7000000 0x00019000 rwx /lib/arm-linux-gnueabihf/ld-2.27.so
0xbefdf000 0xbf000000 0x00000000 rwx [stack]
0xffff0000 0xffff1000 0x00000000 r-x [vectors]
Run command after breakpoint is reached:
gdb$ define hook-stop
Type commands for definition of "hook-stop".
End with a line saying just "end".
>x/64wx 0x606000
>end
Define variable with type:
gdb$ set $i1 = (struct internet*) 0x606000
gdb$ print *$i1
$2 = {piroity = 1, name = 0x0}
Set breakpoint on read of memory address:
gdb$ rwatch *0xfeedface
Hardware read watchpoint 2: *0xfeedface
Set breakpoint on read or write of memory address:
gdb$ watch *0xfeedface
Disable ASLR:
gef➤ aslr off
[+] Disabling ASLR
Figure out what is at an address anywhere in memory:
gef➤ telescope 0x7ffe48142898
0x00007ffe48142898│+0x0000: 0x00007ffe4814293f → 0x0000000040103c00 ← $rsi
0x00007ffe481428a0│+0x0008: 0x0000000000000000
0x00007ffe481428a8│+0x0010: 0x00007ffe48142979 → 0x5900007ffe481432
0x00007ffe481428b0│+0x0018: 0x00007ffe48142940 → 0x000000000040103c → add rbp, rbx
0x00007ffe481428b8│+0x0020: 0x0000000000000000
0x00007ffe481428c0│+0x0028: 0xfffffffffffffff8
0x00007ffe481428c8│+0x0030: 0x0068732f6e69622f ("/bin/sh"?)
0x00007ffe481428d0│+0x0038: 0x000000000000003b (";"?)
0x00007ffe481428d8│+0x0040: "qaaaraaasaaataaauaaavaaawaaaxaaayaaazaabbaabcaabda[...]"
0x00007ffe481428e0│+0x0048: "saaataaauaaavaaawaaaxaaayaaazaabbaabcaabdaabeaabfa[...]"