Microsoft has released out-of-band updates for Windows 7 and Windows Server 2008 R2 to address a serious privilege escalation vulnerability introduced earlier this year by the Meltdown mitigations.

Researcher Ulf Frisk reported this week that the patches released by Microsoft in January and February for the Meltdown vulnerability created an even bigger security hole that allows an attacker to read from and write to memory at significant speeds.

Frisk disclosed details of the bug since Microsoft’s security updates for March appeared to have addressed the issue. However, an investigation conducted by the tech giant revealed that the flaw had not been properly fixed.

Microsoft informed customers on Thursday that a new patch has been released for Windows 7 x64 Service Pack 1 and Windows Server 2008 R2 x64 Service Pack 1 to fully resolve the problem. “Customers who apply the updates, or have automatic updates enabled, are protected.” a Microsoft spokesperson said.

The vulnerability, tracked as CVE-2018-1038 and rated “important,” has been patched with the KB4100480 update. Users are advised to install the update as soon as possible, particularly since some Microsoft employees believe it will likely be exploited in the wild soon.

“An elevation of privilege vulnerability exists when the Windows kernel fails to properly handle objects in memory. An attacker who successfully exploited this vulnerability could run arbitrary code in kernel mode. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights,” Microsoft said in an advisory.

Frisk explained in a blog post that while the Meltdown vulnerability allows an attacker to read megabytes of data per second, the new flaw can be exploited to read gigabytes of data per second. In one of the tests he conducted, the researcher managed to access the memory at speeds of over 4 Gbps. The security hole can also be exploited to write to memory.

Exploiting the flaw is easy once the attacker has gained access to the targeted system. A direct memory access (DMA) attack tool developed by Frisk can be used to reproduce the vulnerability.

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