[egeozcan]

I wonder why Windows Defender has the privilege to alter the system files. Read them for analysis? Sure! Reset (as in, call some windows API to have it replaced with the original), why not? But being able to write sounds like a bad idea.

However, I don't know what I'm talking about so take it with a grain of salt!

[EvanAnderson]

AV had traditionally run as SYSTEM on Windows (and, in the past, often had kernel mode drivers too). I've always thought it was a terrible idea. It opens up exciting new attack surfaces. Kaspersky and McAfee both had privilege escalation vulnerabilities that I can recall. There have been a ton in multiple products over the years.

[labelbabyjunior]

They kind of have to, though.

If malware exploits a privilege escalation vuln, what's the AV going to do about it when it's reduced to the software equivalent of a UK police officer? Observe and report? Stop or I'll say "stop" again?

AV requires great power, which requires great responsibility. The second part is what often eludes AV developers.

[EvanAnderson]

The OS should do the SYSTEM-level lifting and scanning processes and behavior analysis should run sandboxed as low priv processes. It would require a clearly defined API and I feel like MSFT was always reticent to commit, leaving AV manufacturers to create hacky nightmares.

[labelbabyjunior]

Well the OS should do nothing—remember MS was taken to court over that—but better privsep on the part of the AV, sure.

Technically, Defender can be replaced with 3rd party AV.

[bux93]

Windows has separate SeBackupPrivilege for backup software, so why not for AV?

[arcfour]

What would this privilege look like that is meaningfully different from SYSTEM while being properly protected from/able to deal with malware that has an LPE?

[formerly_proven]

“Because the remediation component requires SYSTEM, the entire AV needs to run as SYSTEM and we have to unpack malware in the kernel”

[Fokamul]

Because to get Ring0, you just need signed vulnerable driver.

There are tons of signed drivers to explore ;-)

[labelbabyjunior]

Some files under Windows are protected as the TrustedInstaller user, which is a more restrictive level of permissions than SYSTEM.