Not all Windows releases receive the same treatment when it comes to security patches, leaving some users exposed to known vulnerabilities, security researchers from Google’s Project Zero team warn.
The researchers explain that, because Microsoft silently patches reported vulnerabilities in major Windows 10 releases, such as the Creators Update or the Fall Creators Update, Windows 8 and Windows 7 users become exposed to vulnerabilities that affect their platform iterations as well.
The issue is that attackers can compare patched Windows 10 builds with the previous, unpatched builds to discover the addressed issues and then target older and still vulnerable platform iterations. By comparing the builds, attackers can discover the vulnerabilities and technical details surrounding them.
Called patch diffing, the technique of comparing binaries is also employed to discover so-called 1-day bugs, or vulnerabilities affecting users who are slow to install security patches, Mateusz Jurczyk of Google Project Zero explains.
Another technique that attackers can use is binary diffing, which allows them to discover differences between “two or more versions of a single product, if they share the same core code and coexist on the market, but are serviced independently by the vendor.”
The Windows operating system is one product binary diffing can be used on, as it currently has three versions under active support, namely Windows 7, 8, and 10. Despite Windows 7 having the largest desktop market share at the moment, at nearly 50%, only the most recent platform iteration is receiving structural security improvements.
“This creates a false sense of security for users of the older systems, and leaves them vulnerable to software flaws which can be detected merely by spotting subtle changes in the corresponding code in different versions of Windows,” the security researcher says.
In a blog post, Jurczyk shows how binary diffing was used “to find instances of 0-day uninitialized kernel memory disclosure to user-mode programs.” Such issues can be used in local privilege escalation exploit chains or to expose sensitive data stored in the kernel address space, he argues.
“Security-relevant differences in concurrently supported branches of a single product may be used by malicious actors to pinpoint significant weaknesses or just regular bugs in the more dated versions of said software. Not only does it leave some customers exposed to attacks, but it also visibly reveals what the attack vectors are, which works directly against user security,” Jurczyk notes.
Contacted by SecurityWeek, a Microsoft spokesperson provided the following statement: “Windows has a customer commitment to investigate reported security issues, and proactively update impacted devices as soon as possible. Additionally, we continually invest in defense-in-depth security, and recommend customers use Windows 10 and the Microsoft Edge browser for the best protection.”
Patches aimed to address the specific vulnerabilities Google’s researcher mentions in his post were released to all supported Windows versions, the Microsoft spokesperson also pointed out.