Notices by Will Dormann (wdormann@infosec.exchange)

@cstross @lproven
... AND you're willing to pay $30 per year.

Merely installing Windows 10 LTSC will get you just over a year extra mainstream (free) security updates. If you install Windows 10 IoT LTSC and you jump through the hoops of setting up ESU and also pay $30 for each year of support, sure, you'll continue to get security updates.

@mimir @GossiTheDog
You're asking Kevin if the blog post that he wrote is good? And suggesting that it might be AI-generated? 🤦♂️

@FritzAdalis @mimir @GossiTheDog

Ahh, I totally missed that! I only read the DoublePulsar writeup didn't notice the linked-to page.

There’s a good write up here

😬

Probably best to wipe that from your post, Kevin. And we'll pretend that it was never there. 😂

One of these seems different than the other, but I can't quite put my finger on it... 🤔

Would changing the ACLs to not allow non-admin users the ability to create directories off of C:\ really have a real-world impact of limiting LPEs?

Absolutely. When you write a tool to look for things (e.g. Crassus), you see things. Heck, I've seen a privileged service attempt to open files in C:\Program%20Files\, which any non-admin Windows user can create by default.

But no, even despite being presented with evidence for how this could fix an entire CLASS of LPEs on Windows, MSRC was not interested.

So, apparently this is the "fix" for CVE-2025-21204. Microsoft recently updated their advisory to say what the update does.

Prior to everybody freaking out, the advisory for CVE-2025-21204 said nothing about what it does.

Two gripes:

1. MSRC publishing content-free advisories has consequences, but they never seem to appreciate this.
2. I told MSRC YEARS AGO that they can avoid an entire class of LPE vulnerabilities in 3rd-party software and their own software by not allowing non-admin users to be able to create directories off of C:\. They refused to make any change because it might "break things".

Great job, folks.

From over at the Bad Site ™
Both the vulnerability and the "fix" for CVE-2025-21204 are quite silly.

The scenario is:

1. Non-admin user creates C:\inetpub\wwwroot directory and puts web content there
2. Admin user at some point in the future enables IIS on the system.

The outcome is:
The web content provided by the non-admin user (be it a web shell or whatnot) is served up by IIS.

Maybe non-admin users shouldn't be able to make directories or junctions (to directories or files) in C:\?
NAH.

Maybe installing IIS should provide a clean webroot when it's installed?
NAH.

Just preemptively make a C:\inetpub directory that non-admin users can't write to. That fixes the problem. 🤦♂️

Microsoft blocks ActiveX by default in Microsoft 365, Office 2024
https://www.bleepingcomputer.com/news/microsoft/microsoft-blocks-activex-by-default-in-microsoft-365-office-2024/

About damn time!

Upon further investigation, because that's how I am, I've confirmed that Hyper-V (on a completely different host system) behaves the same as VMware for me. The heap spray ends up at addresses to high to allow exploitation.

But for Stephen, both VMware- and Hyper-V-based ICS systems start heap spraying low enough to allow exploitation.

Neither one of us can figure out why this is the case.

Why am I seeing a difference with my heap allocation addresses vs. what Stephen is seeing?

"Easy"

I'm using VMware, and Stephen is using Hyper-V.

Looking at the e820 info when the VM boots, we can see that with a VMware VM, we have a couple of ACPI entries, and then the usable section after that starts at 0xbff00000. With Hyper-V, there is no ACPI section, and the usable section merely starts at 0x00100000. Also looking at the /proc/iomem output, we can see a clear difference between memory layout in a Hyper-V VM vs. a VMware VM.

What are the consequences of this?
An ICS VM that is running on a default VMware configuration will presumably not be exploitable using the Rapid7 technique. However one running on Hyper-V will be. 🤔

Edit All of the above is a red herring, as I don't know how computers work.

Well this is hilarious. When looking closer at Stephen's screenshot, I noticed that he was running Ruby from Windows. That couldn't make a difference, could it??

YES. If you run the PoC exploit from Windows, heap allocations will start at a low address and the exploit will work just fine. If you run the PoC exploit from Linux (I used Ubuntu), then the heap allocations will happen at a memory range that is too high to work.

I truly have less understanding of how computers work than I could ever have imagined.

Note that if you target an ICS system that has one CPU, you get one web process and ASLR will load libdsplibs.so at a different location every time. So you can guess a fixed address and it'll eventually be correct. But if your target ICS has multiple CPU cores, you'll get a fork()'d (but not exec()'d web process, so the memory layout will be the exact same every time. So the PoC would need to vary the guessed load address of libdsplibs.so for each attempt, rather than relying on the changes of the guess to happen server-side.

Edit: No, as per usual, I've fallen victim to another red herring here.

As I dig deeper into this mystery, I've discovered that I'm (as expected) once again mistaken here.

Yes, the Rapid7 PoC needs Ruby 3.1 or older for it to work right.
But no, there isn't a difference between Linux Ruby and Windows Ruby here.

Why was I steered wrong?
Heap allocations on Linux (ICS) don't simply start at low addresses and grow higher. The allocations will use low addresses if they need to. Why didn't my allocations hit low addresses in all of my early testing? Because my ICS test systems all have multiple cores. Stephen's did not. Also, even in my single-core VMs, I suppose I didn't wait long enough before giving up after notinc allocations happening at high addresses. After seeing allocations happening at high addresses for a while, I incorrectly assumed that low addresses wouldn't be touched.

So if I were correcting this Rapid7 PoC, I would:

1. Have the script itself modify the guessed libdsplibs.so base address. Because the Ivanti web process does a fork() without an exec(), every single re-spawned web process will have the exact same memory layout as its parent. As such, ASLR will only randomize anything in the web process once at boot time, and not per time it crashes.
2. If the target is multi-core, then the heap spray will need to be larger. With the multi-web-process situation you end up with on multi-core ICS systems, the default Rapid7 PoC will not work because any given web process will not get coerced into allocating at low addresses.
3. I'd probably update the script to work with modern Ruby versions. No need to crash upon attempting to figure out the target ICS version.

Just to help you all visualize what's going on here, here's a sped-up animation of the allocations happening in the web process when it receives the Rapid7 heap spray. Note that the low addresses aren't touched until near the end. My impatience to wait for the spray to complete led me to draw the incorrect conclusion that low addresses weren't going to get touched.

@GossiTheDog @faebudo @FritzAdalis @jernej__s
If I remember my testing properly, a junction to a folder does not break the update. But a weird junction to a file (which Microsoft claims is not possible) does break the April update.

Which mirrors the test that a C:\inetpub directory does not break the update but a C:\inetpub file does break things. Except that the junction variant is something a non-admin user can do.

Rapid7 has provided details and a PoC for how to exploit this:
https://attackerkb.com/topics/0ybGQIkHzR/cve-2025-22457

TL;DR: Since you can't steer EIP to something you control directly, you do a heap spray and go the indirect route of a non-limited EIP subversion.

If we poke around with various sizes/contents of the buffer that we send, we can conclude that we can indeed control EIP. (Yes, EIP, since web is a 32-bit app 😂).

However, given that the address space of web has nothing that matches up with ASCII-based number/. addressing, I'm curious what these "sophisticated means" being used ITW are. Maybe something data-based? 🤔

Also LOL at Ivanti's:

it was evaluated and determined not to be exploitable

If I look closer at the difference between the vulnerable version and the "remediated" version, it's now clear where the fix is.

In the vulnerable code, the attacker-provided length of data is strlcopy'd into a 50-byte array. And badness ensues.

In the "remediated" version, the strlcopy only copies 50 bytes, as the target variable is 50 bytes.

So I'd consider this an actual fix. But presumably Ivanti didn't realize that a stack buffer overflow could have a security impact? And thus the lack of CVE when it was fixed, or the attempt to also fix their Ivanti Policy Secure and ZTA Gateways products? 🤷♂️

And per the excellent folks at watchTowr, we can see what the vulnerability is:
A stack buffer overflow in X-Forwarded-For

No need to find a specific endpoint or do something clever. Simply make a web request to anywhere on an ICS system with a large X-Forwarded-For HTTP header and you'll get a stack buffer overflow on the system. 🤦♂️

And due to the fact that the Ivanti web server does a fork() without a corresponding exec(), we get the same memory layout every single time.

Now, about Ivanti's use of remediated... The function where the overflow happens just happens to have been rewritten in a way that avoids the overflow.

Did Ivanti recognize the possibility of a stack buffer overflow and not recognize it as a security issue? Or did they just happen to change code to accidentally avoid the overflow (and decide to use exploit mitigations as well).

You decide...

FWIW, I cannot reproduce the Rapid7 PoC. Per the R7 write-up, they can get around the limitation of only addressing things in the 0x30303030 - 0x39393939 address space (including 0x2e2e2e2e) by doing a heap spray.

But at least in my naive testing on a single VMware VM that I have handy, I cannot get the heap spray to get anywhere near that address range. For me, the spray starts pretty consistently around the 0xcnnnnnnn range.

As such, while the heap spray is indeed succeeding at placing known bytes at guessable locations, the fact that these allocations happen at higher than reachable memory locations makes the heap spray accomplish nothing.

...

@GossiTheDog @Busta
Hilarious.
The two things that MSRC seems to aim to to achieve are:

1. Avoid saying anything about what their security updates do unless their hand is forced.
2. Take the path of "least resistance" as opposed to fixing the root cause of problems. (In this case, non-admins can create subdirectories directly off of C:\)

https://infosec.exchange/@wdormann/114319281111054638

@GossiTheDog
Ah, you'd think that you couldn't.
But indeed you can!
That is, a non-admin user can create a "directory" junction to a file target, which will have the result of April's security updates failing to install. 😂

It seems that this weird concept of a junction to a file achieves an unexpected double-standard:

1. It counts as a directory when it comes to NTFS ACLs (a non-admin user can create a junction in C:\)
2. Depending on how the junction is accessed, it might count as a file as opposed to being treated as a directory.

This seems like a problem. Obviously in the case of April's updates here. But perhaps even more generically in that a junction to a file target seems to almost guarantee unexpected behavior.