May 11, 2026: The Red Sun still prevails.

[wdormann@infosec.exchange]

@jhr77 @christopherkunz
I suspect that Microsoft pushed out Defender updates that mitigate the exploit.

With current definitions, I've not seen RedSun succeed. No matter how long I wait.

With old definitions, success is pretty quick.

[christopherkunz@chaos.social]

@wdormann @jhr77 Huh, that's odd. Works fine for me. Same definitions version.

[gossithedog@cyberplace.social]

@christopherkunz @wdormann @jhr77 do you have cloud protection turned on?

[wdormann@infosec.exchange]

@GossiTheDog @christopherkunz @jhr77
Cloud-delivered protection ?
If so, then yeah, it's on.
It's the same stock Win11 VM that worked in April. Just with Defender updates installed.

[christopherkunz@chaos.social]

@GossiTheDog @wdormann @jhr77 Yes, cloud protection is on. This is a German Win11 Home, I think. After updating to today's definitions and a reboot, RedSun.exe doesn't seem to win the RC anymore, so the reboot was likely necessary to apply the Defender mitigation.
I don't think this is merely a signature update, from what I understood the mitigation requires a core update to Defender.

[wdormann@infosec.exchange]

@christopherkunz @GossiTheDog @jhr77
The executable bits for Defender are updated along with sigs.

[christopherkunz@chaos.social]

@wdormann @GossiTheDog @jhr77 On second attempt, the exploit worked. So whatever MS did, is still not a 100% mitigation. I''ll try again to reproduce what happened.

[wdormann@infosec.exchange]

@christopherkunz @GossiTheDog @jhr77
When it succeeds, does it happen relatively quickly?

I've tried both waiting 10 minutes and have also tried 10 times in a row, and neither strategy is successful on my Win11 VM.

[christopherkunz@chaos.social]

@wdormann @GossiTheDog @jhr77 Reboot, log in, win-r, cmd, cd \temp, RedSun.exe, worked on first attempt.
In my last attempt, I had opened the Defender warning popup "defender has found a threat" and I thought I'd triggered some condition for the exploit to work. Seems not, I can still run it.
It succeeds after about 10 seconds.

[wdormann@infosec.exchange]

@christopherkunz @GossiTheDog @jhr77
The dialog is the detection of the EICAR TieringEngineService.exe and is definitely a part of the successful exploit flow.

It's just that at least for me, it never succeeds with updated defs. ‍️

[christopherkunz@chaos.social]

@wdormann @GossiTheDog @jhr77 Yeah, the first dialog is the detection of EICAR, the second one is the admission of defeat. I get both, and a NT_AUTHORITY shell, on running RedSun.exe.
This is weird, but I suspect we're basically arguing against a ticking clock here. Patch day will land soon and with it, undoubtedly a RedSun mitigation. Actually, let me milk this opportunity for a meme.

[christopherkunz@chaos.social]

@wdormann @GossiTheDog @jhr77 I think my TieringEngineService.exe might be permanently patched/replaced with the RedSun copy and none of the definitions updates have cleaned it up.

[wdormann@infosec.exchange]

@christopherkunz @GossiTheDog @jhr77
Well yep, if you're testing on an already-popped machine, that's an invalid test.

That is, if C:\Windows\system32\TieringEngineService.exe has already been replaced, then the exploit might appear to "work" even when it doesn't.

TieringEngineService.exe is a Windows component. It has nothing to do with Defender, and no Defender update will restore it to its pristine state.

[wdormann@infosec.exchange]

@christopherkunz @GossiTheDog @jhr77

Though I'll also admit that having Windows Security open seems to indicate that Windows Defender stops when RedSun is attempted.

From the GUI it's merely Threat service has stopped, but in Event viewer we can get more info in that it's Microsoft Defender Antivirus has encountered a critical error when taking action on malware or other potentially unwanted software.

It restarts automatically.

If this is an intentional RedSun fix, I'll say that it's less than ideal.

[jhr77@mastodon.social]

@wdormann @christopherkunz @GossiTheDog Hi, today at the first try I had a shell with system rights. So i assume that it worked successfully.

[wdormann@infosec.exchange]

@jhr77 @christopherkunz @GossiTheDog

Just to be clear, before you attempted the exploit, your C:\Windows\system32\TieringEngineService.exe file had a valid signature?

[jhr77@mastodon.social]

@wdormann @christopherkunz @GossiTheDog So this is even worse as this is persistent

[christopherkunz@chaos.social]

@wdormann @jhr77 @GossiTheDog Yeah, mine is unsigned, so I'm doing the whole dism & sfc routine now to presumably fix it.
I'm a little surprised though: Is this normal behavior that unsigned corrupted executables remain indefinitely in \system32 and aren't detected or removed? Is this something I would have to trigger manually, like an offline scan of sorts?

[jhr77@mastodon.social]

@christopherkunz @wdormann @GossiTheDog same same here. It's getting worse when asking more questions. But it was possible to replace with the original version. Hopefully the system is clean now. Maybe making a scan with the defender...

[wdormann@infosec.exchange]

@jhr77 @christopherkunz @GossiTheDog
The exploit made no claims about being temporary.