RedSun: System user access on Win 11/10 and Server with the April 2026 Update

131

aairhangerf15 about 11 hours ago 31 commentsRead Article on github.com

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Discussion (31 Comments)Read Original on HackerNews

egeozcan•about 8 hours ago

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•about 8 hours ago

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•about 8 hours ago

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•about 8 hours ago

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.

bux93•about 6 hours ago

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

formerly_proven•about 5 hours ago

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

Fokamul•about 6 hours ago

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

There are tons of signed drivers to explore ;-)

labelbabyjunior•about 8 hours ago

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

lexicality•about 2 hours ago

helpfully the user provides a second tool which automatically turns off Windows Defender so you can't be affected by this: https://github.com/Nightmare-Eclipse/UnDefend

IFC_LLC•about 4 hours ago

I remember the times when Microsoft had a lot of problems 20 years ago because of Sasser and other viruses that were taking over Windows. They did not have any contenders. Yet they have stopped any software development for 9 months just to re-work their entire codebase to prevent things like direct memory execution and stuff like that. The result of that was Windows XP Service Pack 2. After that thing windows XP became a legend.

Now, when Linux is slowly creeping on one side, and Mac NEO on another they keep releasing this AI-slop.

By the looks of it they make most of their money from the cloud and other software things nowadays. And Windows has become a sidekick in their processes.

toyg•about 2 hours ago

I don't think SP2 made much of a difference in the popularity of XP. It was already dominant, and it's mostly remembered as "legendary" because it had become the target platform for every hardware and software vendor on the planet. Windows 98 was too flaky to engender any serious friction to upgrades, and Windows 2000 was not consumer-friendly enough; XP effectively unified the consumer and professional desktop markets, and became the gold standard.

SP2, if anything, slowed down adoption, since it threw a bunch of spanners in the way of third-party code. It was probably necessary, just to stem the flow of bad press, but no mean a key in XP's overall success.

nailer•about 3 hours ago

> Windows XP Service Pack 2. After that thing windows XP became a legend.

God that was an era. XP SP2 was a great OS, IE was the best browser, MSN was the most popular messenger, Skype was acquired, HTC's Windows CE devices were shipping real web browsers that worked over 3G.

By the end of the Ballmer era, Microsoft has lost the OS, the browser, the messenger, the meeting service and mobile.

hathym•about 6 hours ago

cl /std:c++17 /EHsc /W4 /O2 /DUNICODE /D_UNICODE /wd4005 /Fe:RedSun.exe RedSun.cpp advapi32.lib ole32.lib user32.lib

luma•about 2 hours ago

Tried to download and Defender blocks it.

trollbridge•about 2 hours ago

That's how the exploit works.

luma•about 1 hour ago

I can't seem to find any system files replaced, and the .exe was never executed. I'm running this in a test VM, but from what I can see, Defender signatures have been updated to block this prior to execution.

The exploit, from my reading, needs to be executed in order to do it's thing, but Defender isn't allowing it to be written to the filesystem on download.

ranger_danger•about 9 hours ago

> normally I would just drop the PoC code and let people figure it out

Looks like that's exactly what they did though?

Or maybe they just meant that they don't usually explain how it works?

kijin•about 8 hours ago

Tney gave it a sexy name and set up a website about it (a github repo, at any rate), instead of just talking about it in a mailing list and getting a CVE like a proper bearded security researcher.

tclancy•about 4 hours ago

It’s getting warm above the equator, they may have shaved for the season.

labelbabyjunior•about 8 hours ago

A local privilege escalation to root via an exploitable service?

Doesn't Linux have one of these CVEs...each week?

hnlmorg•about 7 hours ago

Only if you’re running daemons as root. Which would be an idiotic move to begin with because that’s not how distros package their services. So you’d have to intentionally make this mistake.

GuestFAUniverse•about 3 hours ago

Intentionally?

Ignorance is bliss! Simply use docker in its (old) default setup, instead of podman, apptainer, docker-rootless ... and that world is yours.

Added bonuses are the incredible stupid integration with ufw on Ubuntu, images with laughable uid mapping, ...

How that shit got traction baffles me.

BodyCulture•about 6 hours ago

No.

IshKebab•about 4 hours ago

Not quite every week, but yeah it has a lot. And if the target uses sudo at all you don't even need an exploit!

But nobody mentioned Linux. There's no need for whataboutism. They both shouldn't have these vulnerabilities.

hsbauauvhabzb•about 7 hours ago

Probably, but is that service deployed as part of the base operating system or a third party package? Can you remove the service if you deem the crazy service behaviour is unnecessary or too risky for your usecase?