Invalid Code Signature

Adversaries may attempt to mimic features of valid code signatures to increase the chance of deceiving a user, analyst, or tool. Code signing provides a level of authenticity on a binary from the developer and a guarantee that the binary has not been tampered with. Adversaries can copy the metadata and signature information from a signed program, then use it as a template for an unsigned program. Files with invalid code signatures will fail digital signature validation checks, but they may appear more legitimate to users and security tools may improperly handle these files.

Unlike Code Signing, this activity will not result in a valid signature.

Example

CarbonCopy a tool built by paranoidninja for spoofing Digital Signatures, signatures like these can actually bypass AV and pass undetected by analysts because they provide a level of authenticity. See 2 payloads with and without a Digital Signature.

Now will check out the digitally signed one a little more to check what it contains.

A Digital Signature not installed of course this is why we see that it cannot be verified.

We have the option to install this certificate of course with proper permissions but here I am just trying to demonstrate how this "Signature" can provide some level of authenticity since it is Signed by Microsoft, of course a solid analyst can see that this has been valid from a recent Date. So how can we build this digitally signed binary, with CarbonCopy.

Above we see a successful spoofed Signature the requirements for this is very simple the website we are trying to spoof its signature the port the target payload and an output file.

You will also need OSSLSignedCode tool to be installed.

References:

Masquerading as a Windows System Binary Using Digital SignaturesF-Secure Labs