Re: [FD] ELF launcher for encrypted binaries decrypted on-the-fly and executed in memory

[Phil Ashby <Phil.Ashby@xxxxxxxxxx>]

Not a particularly new topic (eg: 
https://reverseengineering.stackexchange.com/questions/3184/packers-protectors-for-linux)
 but always interesting to see new work in the space.

The challenges here IMO are twofold:
- Protecting the key material (a challenge shared with DRM): in this demo its 
not stored but requested via interactive prompt which helps (apart from swap 
space leakage).
- Obfuscating the launcher otherwise it's signature will be the indicator of 
compromise. This becomes a circular problem if the launcher is stored on the 
target, better to inject directly into memory from the remote end?

Cheers,
Phlash.
________________________________
From: Fulldisclosure <fulldisclosure-bounces@xxxxxxxxxxxx> on behalf of 
RedTimmy Security <redazione@xxxxxxxxxxx>
Sent: 01 March 2020 15:05
To: fulldisclosure@xxxxxxxxxxxx <fulldisclosure@xxxxxxxxxxxx>
Subject: [FD] ELF launcher for encrypted binaries decrypted on-the-fly and 
executed in memory

Hi all,
think about a typical Red Team operation, in which tools that commonly trigger 
security alerts to SOC, such as “procmon” or “mimikatz”, are uploaded in a 
compromised machine and then launched without having antivirus, antimalware or 
endpoint protection solutions complaining about that.

There are several ways this could be achieved. The most comprehensive one is 
probably to encrypt the whole ".text" section of a binary and find a way to 
decrypt it on-the-fly in memory at runtime, just before the code is executed. 
The binary should live in encrypted form in the filesystem so that no static 
analysis would be possible even if identified and copied somewhere else. It 
should be only decrypted on the fly in memory when executed, in order to 
prevent dynamic analysis too, unless the decryption key is known. Easier to say 
than to do.

First, "text" is not the only section where valuable information can be 
retrieved. The content of relocations and dynamic symbol tables are places to 
look at too. Their analysis is normally enough to reveal the nature of the 
binary itself. A way to circumvent this fact has to be found.

Similarly, ".rodata" and ".data" are valuable sources of information and 
nothing more than the "strings" command is necessary to get this information 
out of a binary. For example when symbols are resolved at runtime with dlopen() 
and dlsyms(), the string of the function to be resolved lives in the ".rodata" 
section.

We have considered all these factors and described a method for the decryption 
at runtime of ELF binaries in a blog post: 
https://www.redtimmy.com/red-teaming/blue-team-vs-red-team-how-to-run-your-encrypted-binary-in-memory-and-go-undetected/<https://protect-eu.mimecast.com/s/ngiyCVOMkhP9B6msQbdV6?domain=redtimmy.com>

The proof of concept code (golden-frieza project) can be found on github: 
https://github.com/redtimmy/golden-frieza<https://protect-eu.mimecast.com/s/XdAfCW6NlsyG3KZipahbe?domain=github.com>

regards

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