Security Experts:

Windows Security Update Causing System Crash

A recent security bulletin released by Microsoft as part of the August 2014 Patch Tuesday can lead to a crash on some systems, the company said in a knowledge base article.

Microsoft launched an investigation after a large number of users reported getting a so-called "blue screen of death" (BSOD) after installing update KB2982791 (MS14-045).

MS14-045 fixes three Windows kernel-mode driver vulnerabilities that can be exploited by a local authenticated attacker to escalate privileges by running a specially crafted application. However, Microsoft says there are three known issues with this update: fonts are not installed in the default directory, fonts do not render correctly, and the system could crash with a 0x50 Stop error message (bugcheck).

The system crash and the font rendering issue can also occur if the KB2970228 (new Russian Ruble currency symbol), the KB2975719 (August 2014 update rollup for RT 8.1, 8.1, and Server 2012 R2) or the KB2975331 (August 2014 update rollup for RT, 8, and Server 2012) updates have been installed.

"Apparently, the BSoD is caused by incorrect handling of the Windows font cache file - and because that happens during boot-up, you end up stuck in a reboot loop," Sophos' Paul Ducklin explained in a blog post. "The euphemistically-named 'bugcheck' number that you'll see if you are affected is: 0x50 PAGE_FAULT_IN_NONPAGED_AREA.

The expert says Microsoft missed the bug in testing because it is triggered only in specific circumstances.

"You need to have one or more OpenType Font (OTF) files, installed in non-standard font directories, that are recorded in the registry with fully-qualified filenames," Ducklin noted.

While the flaws are being investigated, Microsoft has removed the download links to affected updates. The company has also published a workaround, but regular users might find it difficult to apply. Those who are not certain if the buggy updates have been installed on their systems can use a PowerShell script written by Edward Langley of the Naked PowerShell blog to determine if they have to take any steps.

The security bulletins released on August 12 address a total of 37 vulnerabilities affecting Windows, Internet Explorer, .NET, SQL Server, OneNote, Office, SharePoint and other software.

Earlier this month, Microsoft announced that with the August 12 updates Internet Explorer would start blocking outdated ActiveX controls such as Java. However, after receiving feedback from customers, the company decided to push the date to September 9, when the security updates for next month will be released.

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Eduard Kovacs is an international correspondent for SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.