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31-days-of-API-Security-Tips

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This challenge is Inon Shkedy's 31 days API Security Tips.

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# 31-days-of-API-Security-Tips

### This challenge is Inon Shkedy's 31 days API Security Tips

#### -API TIP: 1/31-

*Older APIs versions tend to be more vulnerable and they lack security mechanisms.
Leverage the predictable nature of REST APIs to find old versions.
Saw a call to `api/v3/login`? Check if `api/v1/login` exists as well. It might be more vulnerable.*

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#### -API TIP: 2/31-

*Never assume there’s only one way to authenticate to an API!
Modern apps have many API endpoints for AuthN: `/api/mobile/login` | `/api/v3/login` | `/api/magic_link`; etc..
Find and test all of them for AuthN problems.*

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#### -API TIP:3/31-

*Remember how SQL Injections used to be extremely common 5-10 years ago, and you could break into almost every company?
BOLA (IDOR) is the new epidemic of API security.
As a pentester, if you understand how to exploit it, your glory is guaranteed.*

> Learn more about BOLA : [https://medium.com/@inonst/a-deep-dive-on-the-most-critical-api-vulnerability-bola-1342224ec3f2](https://medium.com/@inonst/a-deep-dive-on-the-most-critical-api-vulnerability-bola-1342224ec3f2)
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#### -API TIP: 4/31-

Testing a Ruby on Rails App & noticed an HTTP parameter containing a URL?
Developers sometimes use "Kernel#open" function to access URLs == Game Over.
Just send a pipe as the first character and then a shell command (Command Injection by design)

> Learn more about the open function: [https://apidock.com/ruby/Kernel/open](https://apidock.com/ruby/Kernel/open)
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#### -API TIP:5/31-

*Found SSRF? use it for:*
* Internal port scanning
* Leverage cloud services(like 169.254.169.254)
* Use http://webhook.site to reveal IP Address & HTTP Library
* Download a very large file (Layer 7 DoS)
* Reflective SSRF? disclose local mgmt consoles

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#### -API TIP: 6/31-

*Mass Assignment is a real thing.
Modern frameworks encourage developers to use MA without understanding the security implications.
During exploitation, don't guess object's properties names, simply find a GET endpoint that returns all of them.*
![Infographic](https://pbs.twimg.com/media/ENpsW25XYAAjEJE?format=jpg)

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#### - API TIP: 7/31 -

*A company exposes an API for developers?
This is not the same API which is used by mobile / web application. Always test them separately.
Don't assume they implement the same security mechanisms.*

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#### - API TIP: 8/31 -

Pentest for REST API? Give it a chance and check if the API supports SOAP also.
Change the content-type to "application/xml", add a simple XML in the request body, and see how the API handles it.

> Sometimes the authentication is done in a different component that is shared between REST & SOAP APIs == SOAP API may support JWT

> If the API returns stack trace with a DUMPling, it's probably vulnerable**

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#### - API TIP: 9/31 -

*Pentest for APIs?  Trying to find BOLA (IDOR) vulnerabilities? IDs in the HTTP bodies/headers tend to be more vulnerable than IDs in URLs. Try to focus on them first.*

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#### -API TIP: 10/31-

*Exploiting BFLA (Broken Function Level Authorization)?
Leverage the predictable nature of REST to find admin API endpoints!
E.g: you saw the following API call `GET /api/v1/users/<id>`
Give it a chance and change to `DELETE / POST to create/delete users.`*

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#### - API TIP: 11/31 -

*The API uses Authorization header? Forget about CSRF!
If the authentication mechanism doesn't support cookies, the API is protected against CSRF by design.*

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#### -API TIP : 12/31-

*Testing for BOLA (IDOR)?
Even if the ID is GUID or non-numeric, try to send a numeric value.
For example: `/?user_id=111` instead of `user_id=inon@traceable.ai`
Sometimes the AuthZ mechanism supports both and it's easier the brute force numbers.*

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#### -API TIP: 13/31-

*Use Mass Assignment to bypass security mechanisms.
E.g., "enter password" mechanism:
- `POST /api/reset_pass` requires old password.
- `PUT /api/update_user` is vulnerable to MA == can be used to update pass without sending the old one (For CSRF)*

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#### - API TIP: 14/31 -

*Got stuck during an API pentest? Expand your attack surface! Find sub/sibling domains using http://Virustotal.com & http://Censys.io. 
Some of these domains might expose the same APIs with different configurations/versions.*

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#### -API TIP:15/31-

*Static resource==photo,video,..
Web Servers(IIS, Apache) treat static resources differently when it comes to authorization.
Even if developers implemented decent authorization, there's a good chance you can access static resources of other users.*

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#### -API TIP: 16/31-

Even if you use another web proxy, always use Burp in the background. 
The guys at @PortSwigger
 are doing a really good job at helping you manage your pentest.
Use the “tree view” (free version) feature to see all API endpoints you’ve accessed.

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#### -API TIP:17/31-

*Mobile Certificate Pinning?
Before you start reverse engineering & patching the client app, check for both iOS & Android clients and older versions of them.
There's a decent chance that the pinning isn't enabled in one of them. Save time.*

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#### -API TIP: 18/31-

*Companies & developers tend to put more resources (including security) into the main APIs.
Always look for the most niche features that nobody uses to find interesting vulnerabilities.
`POST /api/profile/upload_christmas_voice_greeting`*

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#### -API TIP:19/31-

*Which features do you find tend to be more vulnerable?*
*I'll start:*
* Organization's user management 
* Export to CSV/HTML/PDF 
* Custom views of dashboards 
* Sub user creation&management 
* Object sharing (photos, posts,etc)

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#### - API TIP:20/31-

*Testing AuthN APIs?
If you test in production, there's a good chance that AuthN endpoints have anti brute-force protection.
Anyhow, DevOps engineers tend to disable rate limiting in non-production environments. Don't forget to test them :)*

> A good example of this issue: Facebook Breach (Found by @sehacure) [http://www.anandpraka.sh/2016/03/how-i-could-have-hacked-your-facebook.html](http://www.anandpraka.sh/2016/03/how-i-could-have-hacked-your-facebook.html)
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#### -API TIP:21/30-

*Got stuck during an API pentest? Expand the attack surface! 
Use http://archive.com, find old versions of the web-app and explore new API endpoints. 
Can't use the client? scan the .js files for URLs. Some of them are API endpoints.*

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#### -API TIP:22/31-

*APIs tend to leak PII by design.
BE engineers return raw JSON objects and rely on FE engineers to filter out sensitive data.
Found a sensitive resource (e.g, `receipt`)? Find all the EPs that return it: `/download_receipt`,`/export_receipt`, etc..*

> Some of the endpoints might leak excessive data that should not be accessible by the user.

> This is an example for OWASP Top 10 For APIs - #3 - Excessive Data Exposure
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#### -API TIP:23/31-

*Found a way to download arbitrary files from a web server? 
Shift the test from black-box to white-box.
Download the source code of the app (DLL files: use IL-spy; Compiled Java - use Luyten)
Read the code and find new issues!*

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#### -API TIP:24/31-

*Got stuck during an API pentest? Expand your attack surface!
Remember: developers often disable security mechanisms in non-production environments (qa/staging/etc); 
Leverage this fact to bypass AuthZ, AuthN, rate limiting & input validation.*

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#### -API TIP:25/31-

*Found an "export to PDF" feature? 
There's a good chance the developers use an external library to convert HTML --> PDF behind the scenes.
Try to inject HTML elements and cause "Export Injection".*

> Learn more about Export Injection: [https://medium.com/@inonst/export-injection-2eebc4f17117](https://medium.com/@inonst/export-injection-2eebc4f17117) 
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#### -API TIP:26/31-

*Looking for BOLA (IDOR) in APIs? got 401/403 errors?
AuthZ bypass tricks:*
* Wrap ID with an array` {“id”:111}` --> `{“id”:[111]}`
* JSON wrap `{“id”:111}` --> `{“id”:{“id”:111}}`
* Send ID twice `URL?id=<LEGIT>&id=<VICTIM>`
* Send wildcard `{"user_id":"*"}`
 
> In some cases, the AuthZ mechanism expects a plain string (an ID in this case), and if it receives a JSON instead it won't perform the AuthZ checks. Then, when the input goes to the data fetching component, it might be okay with a JSON instead of string(e.g: it flattens the JSON)
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#### -API TIP:27/31-

*BE Servers no longer responsible for protecting against XSS.
APIs don't return HTML, but JSON instead.
If API returns XSS payload? - 
E.g: `{"name":"In<script>alert(21)</script>on}`
That's fine! The protection always needs to be on the client side*

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#### -API TIP:28/31-

*Pentest for .NET apps? Found a param containing file path/name? Developers sometimes use "Path.Combine(path_1,path_2)" to create full path. Path.Combine has weird behavior: if param#2 is absolute path, then param#1 is ignored.*
##### Leverage it to control the path

> Learn more: [https://www.praetorian.com/blog/pathcombine-security-issues-in-aspnet-applications](https://www.praetorian.com/blog/pathcombine-security-issues-in-aspnet-applications)
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#### -API TIP:29/30-

*APIs expose the underlying implementation of the app.
Pentesters should leverage this fact to better understand users, roles, resources & correlations between them and find cool vulnerabilities & exploits.
Always be curious about the API responses.*

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#### -API TIP:30/31-

*Got stuck during an API pentest? Expand your attack surface! 
If the API has mobile clients, download old versions of the APK file to explore old/legacy functionality and discover new API endpoints.*

> Remember: companies don’t always implement security mechanisms from day one && DevOps engineers don’t often deprecate old APIs. Leverage these facts to find shadow API endpoints that don’t implement security mechanism (authorization, input filtering & rate limiting)

> Download old APK versions of android apps: [https://apkpure.com](https://apkpure.com)
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#### -API TIP: 31/31-

*Found a `limit` / `page` param? (e.g: `/api/news?limit=100`) It might be vulnerable to Layer 7 DoS. Try to send a long value (e.g: `limit=999999999`) and see what happens :)*

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## Source

#### All of this information is taken from twitter of Inon Shkedy
##### Links: 
* [Inon Shkedy](https://twitter.com/inonshkedy)
* [Traceableai](https://twitter.com/traceableai/)
* [OWASP API PROJECT](https://github.com/OWASP/API-Security)

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