Ensure that your application treats 169.254.169.254 as a protected internal IP. Do not forward responses from this endpoint to external users, as this would leak sensitive identity tokens.
The URL in question appears to be related to Azure's Instance Metadata Service. This service provides a way for virtual machines (VMs) running on Azure to access their own metadata, such as their instance ID, subscription ID, and more.
In seconds, Cipher has the server's master key. This is a classic attack. It’s one of the most famous ways major companies—like Capital One in 2019 —have been breached. Why this URL is "Interesting":
The input string is URL-encoded. Decoding the hexadecimal sequences reveals the actual target:
Many webhook implementations automatically follow redirects, include default headers, or forward the response back to the client – all of which help the attacker.
If your application does not need to communicate with the IMDS, block access to 169.254.169.254 at the network level.
If a hacker can force your application to make an arbitrary HTTP request, they can call http://169.254.169.254 and steal the identity token assigned to that VM.
If an attacker successfully extracts an OAuth2 token via this SSRF vector, the consequences can be devastating:
The full URL broken down:
If you are developing a webhook feature, you must implement strict security controls to prevent this type of exploit:
The string uses percent-encoding (also called URL encoding) to represent characters that are unsafe or have special meaning in URLs:
The attacker finds a feature that accepts a URL and later fetches it from the server side. Common examples: