Feeds

Microsoft fortifies Windows 7 kernel with overrun buster

Safe unlinking coming to a PC near you

The Power of One eBook: Top reasons to choose HP BladeSystem

Microsoft engineers have fortified the latest version of Windows with a feature designed to make it significantly harder for attackers to exploit bugs that may be lurking deep inside the operating system.

The safeguard is called safe unlinking, and it's been dropped into a part of the Windows 7 kernel that allocates and deallocates chunks of memory. Safe unlinking performs a series of checks before entries are removed to make sure attackers aren't trying to exploit the operating system using what's known as a pool overrun.

"This simple check blocks the most common exploit technique for pool overruns," Peter Beck, a member of Microsoft's Security Science team writes here. "It doesn't mean pool overruns are impossible to exploit, but it significantly increases the work for an attacker."

During the past five years or so, Microsoft has added protections such as Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR) to the Windows user mode, to make it harder for attackers to exploit bugs in browsers and other applications. With the percentage of security bulletins affecting the Windows kernel rising from under five percent in 2007 to more than 10 percent last year, Microsoft decided it was time to add the protection to the kernel.

Pool overruns are to the kernel as buffer overruns are to applications. The attacks work by manipulating doubly linked lists of memory entries, in which each block points to the previous and next entry in the list. By causing a chunk of memory to point to a tainted section of code, attackers can escalate privileges of the operating system.

Safe unlinking aims to make such exploits harder by deallocating a block only after checking the integrity of the new memory structure. If it doesn't check out, Windows returns a fatal error. Similar checks were introduced into the user-mode of Service Pack 2 of Windows XP, with additional measures added to Windows Vista.

With most Windows exploits targeting the heap, this latest addition shouldn't be viewed as the same must-have that ASLR and DEP have become. Still, it's hard to find a reason why the safeguard shouldn't be added, particularly in light of Beck's assurance that performance won't take a hit.

"This is smart," said Charlie Miller, who as principal analyst at Independent Security Evaluators has successfully exploited weaknesses in Windows, OS X and Linux. "I think they're trying to stay ahead of the curve." ®

Designing a Defense for Mobile Applications

More from The Register

next story
DARPA-derived secure microkernel goes open source tomorrow
Hacker-repelling, drone-protecting code will soon be yours to tweak as you see fit
How long is too long to wait for a security fix?
Synology finally patches OpenSSL bugs in Trevor's NAS
Don't look, Snowden: Security biz chases Tails with zero-day flaws alert
Exodus vows not to sell secrets of whistleblower's favorite OS
Roll out the welcome mat to hackers and crackers
Security chap pens guide to bug bounty programs that won't fail like Yahoo!'s
HIDDEN packet sniffer spy tech in MILLIONS of iPhones, iPads – expert
Don't panic though – Apple's backdoor is not wide open to all, guru tells us
Researcher sat on critical IE bugs for THREE YEARS
VUPEN waited for Pwn2Own cash while IE's sandbox leaked
Four fake Google haxbots hit YOUR WEBSITE every day
Goog the perfect ruse to slip into SEO orfice
prev story

Whitepapers

Designing a Defense for Mobile Applications
Learn about the various considerations for defending mobile applications - from the application architecture itself to the myriad testing technologies.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Top 8 considerations to enable and simplify mobility
In this whitepaper learn how to successfully add mobile capabilities simply and cost effectively.
Seven Steps to Software Security
Seven practical steps you can begin to take today to secure your applications and prevent the damages a successful cyber-attack can cause.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.