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Questions tagged [gdb]

A source level debugger based on `ptrace` for *NIX systems and developed by the GNU project.

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1answer
26 views

obtaining string value from Unknown elf-x86-64 binary with gdb

I'm trying to find a string value stored in memory by a binary (possibly written in C) that won't show up when I perform "strings a.out". I have tried examining particular memory addresses of interest ...
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1answer
40 views

Gdbserver and idapro

I would like to reverse a file so of an apk using idapro (on windows) and gdbserver(on remote target device) . I arrived until the attach of the running process. But after? Is there a tutorial ...
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64 views

Reverse Engineering Linux Core Dump

I have a Linux Core Dump file for a binary (which apparently crashed during execution) file command on the core dump: core.123: ELF 64-bit LSB core file x86-64, version 1 (SYSV), SVR4-style, from '/...
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0answers
57 views

Techniques for reversing (basic) hash function

Hi I'm relatively new to RE, and I'm using GDB and Radare2. As part of a crackme I'm trying to reverse a weak hash function that's a little too complicated for me to undo by hand. I've been trying to ...
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0answers
22 views

two consecutive mov ops with src and dst reversed. Why? [duplicate]

I'm looking at some assembly code (objdump -D) for a 32-bit binary. I have found main(). Here are two lines in main that I have a question about: 8048a35: 89 45 dc mov %eax,-0x24(%ebp) ...
6
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1answer
168 views

Reverse engineering Windows Defender's signature for Metasploit Framework's metsrv.dll

As a pentester for a consulting agency, it is part of our job to "evade" antivirus after gaining code execution on information systems. It is indeed necessary to prove exploitation of vulnerabilities, ...
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0answers
34 views

Set breakpoint on connect does not find ip

i have one elf64 not stripped malware, in gdb debug, there are functions like open, connect, fgets, socket etc, which function we should first set breakpoint in order to find malicious ip or website? ...
0
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1answer
44 views

gdb for main and input parameters

I have one elf 32 application and not stripped, I use gdb info functions and it list only the memory address and function name, but there is no function name with "main", so any way to find the main ...
0
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1answer
39 views

GDB MI output vs. stdout

I am using GDBs machine interface (mi) to write some simple tracers/loggers. Now I ran into the problem of telling apart GDB output from text the target-program itself wrote to stdout. If I look ...
1
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1answer
45 views

new process id generated during gdb debug

I debug a ELF32 executable in Ubntu 14, I set gdb breakpoint in main, after i click run, the program generate a new process 13050 and exited, I can't use info register to display value and continue ...
2
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2answers
404 views

Find base address and memory size of program debugged in gdb

I want to find out the base address and the imagesize of the program being debugged in gdb. As in, where it got loaded in memory. For shared libraries I can do "info sharedlibrary" and I get very ...
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0answers
41 views

How to break on function call with gdb and no symbol table

I want to debug the Win32 event pumping loop. Thus, I need to put a breakpoint at GetMessage and GetMessageW call. I am using gdb as an asm disassembler on a file with no symbol table. Thus, how to ...
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0answers
29 views

overcome stack offset when a binary is executed in or out of gdb from any path

I try to overcome the stack offset when I execute a target binary in or out of gdb from any path in the system. It is possible ? Or maybe in a first time, just overcome the stack offset when I run ...
1
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1answer
63 views

gdb don't break when I use exec-wrapper script to exec my target binary

Why gdb doesn't break when I use exec-wrapper script to exec my target binary. Here my little test. I use a binary with no pie option to use predictable address. $ gcc -no-pie main.c I have this ...
2
votes
1answer
73 views

Why do we need to know the address of shellcode?

I have read many articles regarding the buffer overflow exploit. Everywhere its written as follow. "It's difficult to know the starting address of the shellcode" Why do we need to know the address ...
2
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2answers
100 views

Can't trace MIPS embedded device remotely

I'm trying to debug a remote device using gdbserver and IDA Pro. I'm attached to the correct PID and I'm able to step through instructions until the point where I redirect $pc to my ROP chain. At the ...
9
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4answers
1k views

How can breakpoint be set using offset in ELF file, not virtual address?

First, generate a simple executable. (ignore the warnings, the executable runs anyway) echo 'main(){puts("123");}'|gcc -x c - -o a Load it with gdb a, then: (gdb) info file Symbols from "/home/...
3
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1answer
379 views

Run a python command with “run” on GDB

Hi I'd like to run a python command python -c 'print "\x90"*52' when the program start in GDB, as I would do when I execute : python -c 'print "\x90"*52' | ./myProg . Does anyone knows any way to ...
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2answers
406 views

How to assemble and inject an instruction with GDB?

GDB has a x/i command (and also disassemble) which allows to view the instructions at a given address. How can we do the reverse – assemble an instruction and write to a given address?
3
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1answer
245 views

Buffer overflow challenge - shell not opening

I'm working on a buffer overflow CTF challenge. The binary for this challenge includes a give_shell function (they cover shellcode in the next challenge) I can successfully overwrite the saved EIP on ...
1
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1answer
436 views

Basic question: how to input non-printable hex values in GDB / NC? [duplicate]

I'm working on a CTF challenge that is an introduction to smashing the stack. I have the binary working in GDB, and can overwrite the correct part of the stack with printable characters. The ...
1
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1answer
2k views

Cannot Access memory error

I am trying to debug a simple buffer overflow program using gdb . I analyzed the program on windows without any issues .But now i am using linux gdb with exact same program but i am getting "Cannot ...
1
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1answer
221 views

Question about gdb and memory addresses

i am trying to use gdb to analyse a c program but i am a little confused. in the above picture you can see i am trying to analyse the stack . On the left we have memory addresses.Since i am using a ...
0
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1answer
269 views

Radare2 cannot debug on windows 7

I downloaded radare 2.5 for windows. I am trying to debug a binary on windows with radare and have tried the following: radare2 -d a.exe fork_and_ptraceme/CreateProcess: The request is not supported. ...
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0answers
45 views

Redirecting gdb output to stdout wihile using pwndbg

I am using pwndbg plugin with gdb. When any program that prints to stdout is run under gdb, I seem to not being able to see the output from the program during the debugging session. How can I redirect ...
1
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1answer
153 views

Break anywhere when $r1 equals to string GDB

Is there anyway to break on gdb where $r1 equals to a certain string I know there is : break [addr] if ((int)strcmp($r1, "hello")) == 0 But what to set in addr when I just wanna break when the r1 is ...
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1answer
318 views

How to set breakpoints in GDB on remote target without an executable?

I'm trying to use a gdb client running on my host machine to talk to a GDB server running on a debug probe. I can connect using the "target remote" command, and I can single step, use monitor ...
0
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0answers
95 views

Set a Breakpoint in an executable type dynamic (ET_DYN)

I am trying to debug an executable marked as a shared object. I know the trick of run it in GDB and stop with CTRL+C, and other tricks from the question How to handle stripped binaries with GDB? No ...
1
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0answers
138 views

Stack buffer overflow SIGSEGV help

I've been going at this for a couple of days now working through trial and error but I can't seem to pinpoint exactly why I'm still getting a SIGSEGV. Here's the stdout of me stepping through the ...
2
votes
1answer
160 views

Debugging Binary using Far Ret to switch Code Segment

It appears that GDB is unable to handle binaries which switch code segments. Using pwntools*, it's trivial to generate a 32-bit intel binary which uses retf to switch to the 64-bit code segment. ...
3
votes
2answers
517 views

Password Bruteforce using angr

I am having a binary which takes an input from user and checks every bit of our character using the check_value function which does some stuff. The disassembly of the interested function is: .text:...
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0answers
423 views

Generating symbol file for closed-source binary by hand

I have a closed-source binary (minecraft-pi). For a given section of the assembly like so: a2ed4: e92d45f8 push {r3, r4, r5, r6, r7, r8, sl, lr} a2ed8: e1a04000 mov ...
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0answers
401 views

My core dump's backtrace stops to a signal handler, what can I do?

I obtained an ELF core dump that was provoked by fuzzing a proprietary server. As I do not have access anymore to the machine that hosted this server, and the server is part of a tightly coupled set ...
1
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1answer
632 views

Why does my shellcode work in gdb but not on the command line

So I just started with reverse engineering and have run into some issues until I recently noticed something strange. I wrote an extremely simple shellcode (exit system call) for practice and I played ...
6
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1answer
871 views

Understanding gdb output

So I was messing with gdb and came across something rather interesting. I ran the following code into gdb: int i, g = 1; for (i = 0; i < 100; i++) g++; Before execution, disas main ...
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0answers
124 views

gdb: How to determine if a function in a .so is ever used in an app

Newbie question about using gdb: I know how to set a breakpoint for a function in a .so file that is actually called from the app using the .so file. This can be done, for instance, using: b ...
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1answer
293 views

Debugging EXE File in Windbg and How to set Breakpoints in Assembly

I am trying to set a breakpoint (created in assembly) and step into an EXE file line by line to watch registers and memory behavior. I have done this easily with gdb under Linux like this. gdb -q ./...
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2answers
214 views

Added instruction to shellcode

I have the following shellcode: xor eax, eax ; eax = 0 push eax ; 0 (end of the string) push 0x68732f2f ; //sh push 0x6e69622f ; /bin mov ebx, esp ; ebx = &(/bin//sh) xor ecx, ecx ...
1
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1answer
309 views

gdb-multiarch Segmentation fault

I've followed the guide from Cross debugging for MIPS ELF with QEMU/toolchain to cross compile a simple hello world application, but for some reason I get a segmentation fault when opening it with gdb-...
4
votes
2answers
334 views

ASM working as is, but not in a C program

I have this piece of ASM: section .text global _start _start: xor eax, eax push eax ; 0 to finish the /bin//sh string push 0x68732f2f ; //sh push 0x6e69622f ; /bin ...
2
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0answers
600 views

IDA Pro GDB QEMU Tricore setup

I have added the lines below to IDA 6.95\cfg\gdb_arch.cfg to try to get QEMU Tricore debugging in IDA Pro, using an ARM tutorial as the basis (page 2): https://www.hex-rays.com/products/ida/support/...
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2answers
514 views

Understanding an if statement in assembly

I have written two simple C programs (one with an if and one without). Looking at the assembly differences there are a few lines that I can't manage to explain and was hoping to get some assistance. ...
1
vote
1answer
441 views

Loading user specified IDA symbols in GDB

While reversing a binary, whatever symbols we name inside IDA IDB database, is it possible to load the same in GDB while debugging? e.g. I tried wsym which attempts to inject those as symbols. However,...
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1answer
213 views

Practicing what SHOULD be a simple crackme. Program calls strlen() but never returns

I'm trying out a crackme from the "LSE CTF" called "Blue Box" worth only 10 points. I've attempted this inside GDB and radare2... It is very simple, takes one argument and first checks to make sure ...
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1answer
205 views

Disassembling code with Hopper

I'm trying to figure out what this code is doing. The first thing that I don't understand is the condition that tests if arg0's value is 0x2. I read that 0x2 in ASCII is STX (Start of text). Here's ...
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1answer
1k views

How to read canary value in gdb?

In a program I am debugging, the canary value is read to eax from gs:0x14 memory location. I am attaching gdb to the process late enough to break on the mov reading the canary to eax. Therefore, ...
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0answers
97 views

What does 'mapped' memory region mean in gdb-peda?

I was reading a write-up of a binary exploitation where I came across the following: What does the mapped keyword listed under Name column mean? What sort of memory region does it refer to?
1
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1answer
489 views

Why can't gdb read memory if pwntools is used to send input?

Here is the program which gdb is attached to: prog.c #include <stdio.h> void dummy(char* s) { } int main() { char buf[512]; scanf("%s", buf); printf("%s\n", buf); dummy(buf);...
3
votes
2answers
1k views

Changing Entrypoint in ELF executable

I wrote some code that does the following: Searches for and finds an offset in a binary file to add code (looks for a sequence of 00s I can overwrite). Then, I change the entrypoint of the ELF to ...
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0answers
142 views

Find string in stripped binary file use gdb

Does this debugger support this feature? Through find it is impossible, as the file stripped.