this post was submitted on 12 Apr 2025
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"According to the research published by Hackmosphere, the technique works by avoiding the conventional execution path where applications call Windows API functions through libraries like kernel32.dll, which then forwards requests to ntdll.dll before making the actual system call to the kernel."

Additional Information:

https://www.hackmosphere.fr/bypass-windows-defender-antivirus-2025-part-1/

https://www.hackmosphere.fr/bypass-windows-defender-antivirus-2025-part-2/

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[–] [email protected] 26 points 2 days ago (1 children)

They also suggest organizations deploy additional security layers beyond Windows Defender, particularly solutions that can monitor behavior at the kernel level.

Anything like this for the typical home user?

[–] [email protected] 29 points 2 days ago (4 children)

Sure, bring back Crowdstrike, that went well...

Btw I wasn't aware XOR was encrytion...

[–] [email protected] 21 points 2 days ago* (last edited 2 days ago) (3 children)

XOR cleartext once with a key you get ciphertext. XOR the ciphertext with the same key you get the original cleartext. At its core this is the way the old DES cipher works.

A bit of useful trivia: If you XOR any number with itself, you get all zeros. You can see this in practice when an assembly programmer XOR's a register with itself to clear it out.

[–] [email protected] 13 points 2 days ago (1 children)

That's how it was done in the old days to save a few cycles in Z80 assembly. XOR A instead of LD A, 0.

[–] [email protected] 3 points 2 days ago

I use that daily in my accelerator work.

Once you learn the trick, you just use it naturally.

[–] [email protected] 5 points 2 days ago

Apple had this undocumented function for screenshotting back on iOS 3.1, and kind of let you use it while waiting for better frameworks in iOS 4.0

At some point they started rejecting your app automatically if they found the symbol for that function in your app. I didn't want to leave my 3.1 users in the dust for no reason, so I did the same trick to obfuscate the symbol name before dynamically linking it in.

It worked right up until they stopped supporting iOS 3.1 completely.

[–] [email protected] 4 points 2 days ago* (last edited 2 days ago) (1 children)

an x86 assembly programmer

Ftfy. not all CPUs have an xor register with itself instruction.

[–] [email protected] 4 points 1 day ago (1 children)

There are a lot more architectures than just x86 that are capable of XORing a register with itself (ie. ARM and RISC-V), and if you took OP to mean the accumulation register specifically, pretty much all CPUs going back as far as I can think have had that functionality.

[–] [email protected] 0 points 1 day ago (1 children)

Yes, but it's not universal that xoring a register with itself is more performant than simply loading it with 0.

[–] [email protected] 2 points 1 day ago (1 children)

I never made that claim, nor did the person you corrected.

[–] [email protected] 1 points 17 hours ago (1 children)

Yes, but that's why x86 assembly programmers do it...

[–] [email protected] 1 points 13 hours ago

No argument there. It's also why it's done in ARM, 8080, SM83, z80, 6502, and basically every other assembly language. It's only not done in RISC-V because you can fold 0 into any instruction as an operand, therefore eliminating the need to clear a register before an instruction.

So why correct the person with a more narrow claim that makes it seem like xor being faster than loading zero is a rarity in CPU architectures? If I said "birds can fly", and your response was "eagles can fly. Ftfy. Not all birds can fly", it would be both true and utterly unhelpful.

[–] [email protected] 12 points 2 days ago

https://en.wikipedia.org/wiki/One_time_pad

XOR may be the only encryption system that cannot be cracked. The length of the key is a PITA though.

[–] [email protected] 6 points 2 days ago (1 children)

It technically counts. It's a cipher that uses the same key for encryption and decryption.

[–] [email protected] 4 points 2 days ago (1 children)

A one time pad, I think it called.

[–] [email protected] 3 points 2 days ago

Btw I wasn't aware XOR was encrytion...

It's even better than ROT13, because you always need to apply ROT13 twice for getting the good results...

[–] [email protected] 3 points 2 days ago (1 children)

That Vitus must be pretty bad.

[–] [email protected] 2 points 1 day ago

Thanks! Fixed!

[–] [email protected] 14 points 2 days ago (1 children)

According to the research published by Hackmosphere, [...]

I cannot find a link to the original research, anybody has the link to the original research?

[–] [email protected] 10 points 2 days ago (1 children)

Wasn’t there something a few months ago about Microsoft handing out secret API calls to developers of other antivirus products so they can quietly disable Defender during the installation of their product? Some guy had this reverse engineered from an installer…

[–] [email protected] 9 points 2 days ago

It’s not a secret. It’s a regkey. You need privs to do it though.

[–] [email protected] 3 points 2 days ago

Saw this attack in the wild this week. Huntress MDR detected and shut it down.