Windows 7 Meltdown patch opens worse vulnerability: Install March updates now

Video: Meltdown-Spectre attack variants discovered

Microsoft's early patches for Intel's Meltdown CPU vulnerability created an even bigger problem in Windows 7 that allowed any unprivileged application to read kernel memory.

Microsoft's January and February patches stopped the Meltdown bug that exposed passwords in protected memory, but security researcher Ulf Frisk has discovered that the patches introduced a far worse kernel bug, which allows any process to read and write anywhere in kernel memory.

Frisk says the vulnerability affects Windows 7 x64 and Windows 2008R2 with the January or February patches.

According to Frisk, the two faulty patches wrongly set a bit in the virtual-to-physical-memory translator known as PLM4 to allow any user-mode application to access the kernel's page tables.

Intel's CPU uses these page tables to translate the virtual memory of a process into physical memory. The correctly set bit would normally ensure the kernel has exclusive access to these tables.

"In short -- the User/Supervisor permission bit was set to User in the PML4 self-referencing entry. This made the page tables available to user mode code in every process. The page tables should normally only be accessible by the kernel itself," he said.

"The PML4 is the base of the 4-level in-memory page table hierarchy that the CPU Memory Management Unit (MMU) uses to translate the virtual addresses of a process into physical memory addresses in RAM."

Download now: IT leader's guide to cyberattack recovery

Also, Frisk says the bug would be "trivially easy" to use to access all physical memory on, due to the PML4 page table being located at a fixed memory address in Windows 7. This situation means an attacker will also be able to locate the Windows 7 page table that is now accessible by user-mode applications.

"Windows 7 already did the hard work of mapping in the required memory into every running process. Exploitation was just a matter of read and write to already mapped in-process virtual memory," writes Frisk.

"Once read/write access has been gained to the page tables it will be trivially easy to gain access to the complete physical memory, unless it is additionally protected by Extended Page Tables (EPTs) used for Virtualization. All one [has] to do is to write [one's] own Page Table Entries (PTEs) into the page tables to access arbitrary physical memory."

Frisk advised all admins and users of Windows 7 and Windows 2008R2 to install Microsoft's March patch to resolve it. Windows 10 and Windows 8.1 are unaffected.

Previous and related coverage

Use HP, Lenovo or Dell? Get ready for new updates to guard against Spectre

Intel's fixed microcode updates to mitigate the Spectre attack have now reached Sandy Bridge and Ivy Bridge chips.

New Spectre attack variant can pry secrets from Intel's SGX protected enclaves

Sensitive data protected by Intel's Software Guard Extensions could be open to a new side-channel attack.

Intel's Spectre fix for Broadwell and Haswell chips has finally landed

Chips that sparked Intel's recall of microcode for Spectre Variant 2 attack now have stable fixes.

First Intel, now AMD also faces multiple class-action suits over Spectre attacks

Customers accuse the chip maker of charging premium prices for a faulty product.

Intel's new Spectre fix: Skylake, Kaby Lake, Coffee Lake chips get stable microcode

Intel makes progress on reissuing stable microcode updates against the Spectre attack.

Meltdown-Spectre: Now the class action suits against Intel are starting to mount up

Intel faces 32 class action lawsuits over its processor flaws and says more may be in the pipeline.

Meltdown-Spectre flaws: We've found new attack variants, say researchers

Intel and AMD may need to revisit their microcode fixes for Meltdown and Spectre.

Linux Meltdown patch: 'Up to 800 percent CPU overhead', Netflix tests show

The performance impact of Meltdown patches makes it essential to move systems to Linux 4.14.

Spectre reboot problems: Now Intel replaces its buggy fix for Skylake PCs

And offers patching tips from US CERT, which it failed to brief on the bugs.

Meltdown-Spectre: Malware is already being tested by attackers

Malware makers are experimenting with malware that exploits the Spectre and Meltdown CPU bugs.

Windows emergency patch: Microsoft's new update kills off Intel's Spectre fix

The out-of-band update disabled Intel's mitigation for the Spectre Variant 2 attack, which Microsoft says can cause data loss on top of unexpected reboots.

Meltdown-Spectre: Why were flaws kept secret from industry, demand lawmakers

Great work on patching your own products, but why were smaller tech companies kept in the dark?

26% of organizations haven't yet received Windows Meltdown and Spectre patches (Tech Republic)

Roughly a week after the update was released, many machines still lack the fix for the critical CPU vulnerabilities.

Bad news: A Spectre-like flaw will probably happen again (CNET)

Our devices may never truly be secure, says the CEO of the company that designs the heart of most mobile chips.