Authentication Bypass & File Upload & Arbitrary File Overwrite

Hello Awesome Hackers, I hope you all doing well!

My name is Souhaib Naceri Or h4x0r_dz Algerian Ethical Hacker.

today I’m sharing a vulnerability that I found a while ago, which I believe is quite interesting.

but I’m not going to share the bug bounty program name & domain name ..etc, because I didn’t get permission to disclose it.

so let’s assume the target is test.com

when I started hunting on the program, I found the admin panel UI bypass

the target uses JSON Web Token (JWT) for the authentication mechanism, and I have put A bit of time into order to understand, trying to find bugs on the bug bounty targets that use JSON Web Token (JWT) .

when you log in to the main website test.comA JSON Web Token (JWT) will be generated for the regular user,

now After I know how the target work, I started doing recon. reading javascript files, running Burp Suite, and clicking on any bottom in the website & also I used Wayback Machine to get all the possible endpoints, and finally subdomain enumeration.

I found The interesting subdomain admin.test.com and now we have come to the interesting part, the admin panel exposes the js file app.js and after I read the whole file 200000 lines of code, I found it uses the JSON Web Token (JWT) for authentication, and I found a list of realm.

but the interesting realm was test-dashboard

The “realm” authentication parameter is reserved for use by authentication schemes that wish to indicate a scope of protection. A protection space is defined by the canonical root URI (the scheme and authority components of the effective request URI;

more info here: https://www.rfc-editor.org/rfc/rfc7235#section-2.2

I used https://jwt.io/ to decode the user Token, and there is a realm=test-user

now I know if I am able to manipulate the realm to test-dashboard I will be able to login to the admin panel, just a feeling.

### steps :

if you decode the jwt you can see the realm has been changed.

now using the manipulated JWT token I’m able to login to the admin panel.

I reported this bug immediately, but this was the expected response from the bug bounty program :

test-staff updated the severity from Critical to Medium

I almost gave up, but I decided to continue digging deeper.

I agree with the Team, to consider the bug critical I need to miniplate the scope in the JSON Web Token (JWT) .

but this is impossible, I need to find 0day and JWT mechanism and any website uses JSON Web Token (JWT) will be vulnerable.

But I’m crazy enough because I start looking for something similar .

since I can control the realm and generate valid JWT, I tried every payload to manipulate the scope, but nothing worked for me and didn’t able to do the escape that I want .

I started doing content discovery using ffuf against admin.test.com but Unfortunately, I didn’t find any valid endpoint,

by default ffuf uses the GET HTTP Method, so I Gave a try to the POST Method. and I found this endpoint https://admin.test.com/upload return 403, it is quite interesting because I found this endpoint in the app.js file.

now, what if I am able to upload a web shell? I got excited

after I spend hours reading the javascript file, I was able to build the file upload request:

but I got a 401 HTTP error :( . Even after I manipulate the realm In JWT

do you know what is Fuzzing ?

if your answer is NO then you miss so many bugs behind you !

Fuzz testing or Fuzzing is a Black Box software testing technique, which basically consists in finding implementation bugs using malformed/semi-malformed data injection in an automated fashion.

I start Fuzzing the Authorization: Bearer <JWT>

and finally, I saw 200 responses :) .

the issue here is when you delete Bearer from the Authorization header You will be able to authenticate in https://admin.test.com. and you will be able to have the admin permission

send this request to upload the file

I go 200 responses with message uploaded

now where I can find the path of my file ??

At first, I thought it is the end, there is no way to know where my file was stored.

I tried the content discovery using ffuf against all the subdomains trying to find something like admin.test.com/uploads/poc.txt

but I didn’t find anything, I start looking into my burp history and reading the response, and I found this href=https://xxxxxxxx.cloudfront.net/gallery/xxxxxxxxx

hmmm, the gallery is the same value at my file upload request at destination input.

I browsed https://XXXXXXXXX.cloudfront.net/gallery/poc.txt

and I found my file is there

Amazon CloudFront is a content delivery network operated by Amazon Web Services. Content delivery networks provide a globally-distributed network of proxy servers that cache content, such as web videos or other bulky media, more locally to consumers, thus improving access speed for downloading the content.

so I can’t upload web shell :( .

even if I report this file upload now, The severity will be very low. again I need to dig deep.

by default Amazon S3 is vulnerable to Misconfiguration Arbitrary File Overwrite if you upload file.txt Amazon S3.

now I have Arbitrary File Overwrite, Now I can do so many things I found that xxxxxxxx.cloudfront.net was used in the main website to host javascript and HTML and other files

so many files are hosted in xxxxxxxx.cloudfront.net , and as an attacker, I can change the content of the files and managed to get stored XSS and other security issues in the main domain, because they used xxxxxxxx.cloudfront.net to host windows software and pdfs, where the user can download, it is a part of the main website,

so I can change the content of these files and gain RCE on the user’s computers by putting malicious codes in the existing EXE or pdf files CSS …etc

the attacker can change other files’ content. the destination parameter in the request body Specify the file path, so I can change any file

first POC file :

We could not verify the vulnerability from the browser due to the cache, so you can CURL

now after I changed the content of the file poc.txt via this requset :

as you can see in my terminal, I was able to over write the existing file.

I got 20k for this vulnerability

also, I got $3,000 for UI admin panel access, 23000$ in total

I hope you learned something new Today, and I’m Really sorry If my write-up was not clear, or if I’m talking too much.

Best regards,