this post was submitted on 12 Apr 2025
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Windows Defender Anti-virus Bypassed Using Direct Syscalls & XOR Encryption (cybersecuritynews.com)
submitted 4 days ago* (last edited 3 days ago) by atrielienz@lemmy.world to c/technology@lemmy.world
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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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[–] QBertReynolds@sh.itjust.works 4 points 3 days 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.

[–] Malfeasant@lemm.ee 0 points 3 days ago (1 children)

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

[–] QBertReynolds@sh.itjust.works 3 points 3 days ago (1 children)

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

[–] Malfeasant@lemm.ee 0 points 2 days ago (1 children)

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

[–] QBertReynolds@sh.itjust.works 1 points 1 day ago (1 children)

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.

[–] Malfeasant@lemm.ee 0 points 1 day ago

Hey look, I'm good at something.