What happens next is up to the program that made the WinINet call. If the proxy server requires authentication, WinINet will get a 407 Proxy Authentication Required response from the server.
If there is no value in this credential store, WinINet will attempt to get the URL through the proxy server. When WinINet connects to a URL (through a proxy server), it first checks its credential store for a username and password. If you configure a proxy server in Internet Explorer, WinINet applications will communicate through it.
#Bypass egress restrictions for cobalt strike beacon stealth windows
WinINet is the Windows Internet API and it’s the library that manages the cache, credential store, and communication for Internet Explorer and other applications. Recently, I decided to look into this problem. Further, let’s assume that these workstations are otherwise isolated from the internet and they also can’t resolve DNS names for external systems. My general advice isn’t bad, but it falls short in this situation: What happens if your target sets up a proxy server that requires the user to authenticate with a separate set of credentials to get out to the internet. Keep in mind, this advice assumes a hardened target. If DNS fails you, then you’re out of luck.
HTTP and HTTPS payloads are fine for transparent proxies or proxy servers that use NTLM authentication. My general advice is this: reverse TCP payloads are a dead option. I previously wrote about why this is a problem and how you might get past different egress restrictions. One of the weakest points for penetration testing tools is their (in-)ability to get past some egress restrictions. I spend a lot of time thinking about what my tools can and can’t do.
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