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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](https://portswigger.net/web-security/ssrf))
Usually you will find that the SSRF is only working in **certain whitelisted domains** or URL. In the following page you have a **compilation of techniques to try to bypass that whitelist**:
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: [https://portswigger.net/web-security/ssrf](https://portswigger.net/web-security/ssrf)
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 server 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 [Gopherus](https://github.com/tarunkant/Gopherus) to create payloads for several services. Additionally, [remote-method-guesser](https://github.com/qtc-de/remote-method-guesser) can be used to create _gopher_ payloads for _Java RMI_ services.
If the SSRF is executed by **curl**, curl has a feature called [**URL globbing**](https://everything.curl.dev/cmdline/globbing) that could be useful to bypass WAFs. For example in this [**writeup**](https://blog.arkark.dev/2022/11/18/seccon-en/#web-easylfi) you can find this example for a **path traversal via `file` protocol**:
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.
## SSRF via SNI data from certificate
The simplest misconfiguration that would allow you to connect to an arbitrary backend would look something like this:
```nginx
stream {
server {
listen 443;
resolver 127.0.0.11;
proxy_pass $ssl_preread_server_name:443;
ssl_preread on;
}
}
```
Here, the SNI field value is used directly as the address of the backend.
With this insecure configuration, we can **exploit the SSRF vulnerability simply by specifying the desired IP or domain name in the SNI field**. For example, the following command would force Nginx to connect to _internal.host.com_:
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**](../xss-cross-site-scripting/server-side-xss-dynamic-pdf.md)**.**
For some exploitations you might need to **send a redirect response** (potentially to use a different protocol like gopher). Here you have different python codes to respond with a redirect:
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If you are having **problems** to **exfiltrate content from a local IP** because of **CORS/SOP**, **DNS Rebidding** can be used to bypass that limitation:
[**`Singularity of Origin`**](https://github.com/nccgroup/singularity) is a tool to perform [DNS rebinding](https://en.wikipedia.org/wiki/DNS\_rebinding) attacks. It includes the necessary components to rebind the IP address of the attack server DNS name to the target machine's IP address and to serve attack payloads to exploit vulnerable software on the target machine.
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** (127.0.0.1 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 www.attacker.com:11211 (the **port must always be the same**).\
To **perform this attack you can use the tool**: [https://github.com/jmdx/TLS-poison/](https://github.com/jmdx/TLS-poison/)\
For **more information** take a look to the talk where this attack is explained: [https://www.youtube.com/watch?v=qGpAJxfADjo\&ab\_channel=DEFCONConference](https://www.youtube.com/watch?v=qGpAJxfADjo\&ab\_channel=DEFCONConference)
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.
**Checking the time** of the responses from the server it might be **possible to know if a resource exists or not** (maybe it takes more time accessing an existing resource than accessing one that doesn't exist)
If you find a SSRF vulnerability in a machine running inside a cloud environment you might be able to obtain interesting information about the cloud environment and even credentials:
* [Blog post on SSRF usage](https://blog.tneitzel.eu/posts/01-attacking-java-rmi-via-ssrf/)
_remote-method-guesser_ is a _Java RMI_ vulnerability scanner that supports attack operations for most common _Java RMI_ vulnerabilities. Most of the available operations support the `--ssrf` option, to generate an _SSRF_ payload for the requested operation. Together with the `--gopher` option, ready to use _gopher_ payloads can be generated directly.
SSRF Proxy is a multi-threaded HTTP proxy server designed to tunnel client HTTP traffic through HTTP servers vulnerable to Server-Side Request Forgery (SSRF).
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