Microsoft patch fails to fix Installer zero-day affecting every version of Windows

The exploit allows hackers to elevate privileges and create admin accounts

Red lock unlocked among several blue locked locks

Cyber criminals are testing out a proof-of-concept malware that targets a zero-day escalation of privilege exploit in the Microsoft Windows Installer.

The flaw, which enables hackers with a limited user account to elevate their privileges to become an administrator, affects every version of Microsoft Windows, including fully patched Windows 11 and Server 2022.

Malware samples have already been detected in the wild that are attempting to take advantage of this vulnerability, according to a blog post by security researchers at Cisco Talos.

It was security researcher Abdelhamid Naceri who initially discovered this elevation of privilege vulnerability and worked with Microsoft to address it. Microsoft then released an update that was intended to fix CVE-2021-41379 on 9 November as part of its monthly security update.

However, the patch failed to fix the vulnerability, and Naceri published a proof-of-concept exploit code on GitHub on 22 Nov that still works despite the fixes implemented by Microsoft.

“The code Naceri released leverages the discretionary access control list (DACL) for Microsoft Edge Elevation Service to replace any executable file on the system with an MSI file, allowing an attacker to run code as an administrator,” said Jaeson Schultz, technical leader for Cisco's Talos Security Intelligence & Research Group.

Related Resource

Multi-factor authentication deployment guide

A complete guide to selecting and deploying your MFA authentication guide

The whitepaper title on a strip of swirling blue and purple diagonal across the pageFree download

According to a posting by Naceri on GitHub, the technique may not work on every installation, because windows installations, such as server 2016 and 2019, may not have the elevation service.

“I deliberately left the code which take over file open, so any file specified in the first argument will be taken over with the condition that SYSTEM account must have access to it and the file mustn't be in use. So you can elevate your privileges yourself,” he said.

Naceri added that the best workaround available at the time of writing this is to wait for Microsoft to release a security patch, due to the complexity of this vulnerability.

“Any attempt to patch the binary directly will break windows installer. So you better wait and see how Microsoft will screw the patch again,” he said.

Featured Resources

Shining light on new 'cool' cloud technologies and their drawbacks

IONOS Cloud Up! Summit, Cloud Technology Session with Russell Barley

Watch now

Build mobile and web apps faster

Three proven tips to accelerate modern app development

Free download

Reduce the carbon footprint of IT operations up to 88%

A carbon reduction opportunity

Free Download

Comparing serverless and server-based technologies

Determining the total cost of ownership

Free download

Recommended

Microsoft Defender review: Effective, effortless protection for zero cost
antivirus

Microsoft Defender review: Effective, effortless protection for zero cost

3 Dec 2021
BazarLoader malware abuses Windows 10 apps in 'Call Me Back' attack
phishing

BazarLoader malware abuses Windows 10 apps in 'Call Me Back' attack

12 Nov 2021
How to fix a stuck Windows 10 update
operating systems

How to fix a stuck Windows 10 update

10 Nov 2021
17 Windows 10 problems - and how to fix them
operating systems

17 Windows 10 problems - and how to fix them

29 Oct 2021

Most Popular

What should you really be asking about your remote access software?
Sponsored

What should you really be asking about your remote access software?

17 Nov 2021
What are the pros and cons of AI?
machine learning

What are the pros and cons of AI?

30 Nov 2021
How to move Microsoft's Windows 11 from a hard drive to an SSD
Microsoft Windows

How to move Microsoft's Windows 11 from a hard drive to an SSD

24 Nov 2021