Microsoft shuts down zero-day exploit on September Patch Tuesday

Microsoft shut down a zero-day vulnerability launched by a Twitter user in August and a denial-of-service flaw on September Patch Tuesday.

A security researcher identified by the Twitter handle SandboxEscaper shared a zero-day exploit in the Windows task scheduler on Aug. 27. Microsoft issued an advisory after SandboxEscaper uploaded proof-of-concept code on GitHub. The company fixed the ALPC elevation of privilege vulnerability (CVE-2018-8440) with its September Patch Tuesday security updates. A malicious actor could use the exploit to gain elevated privileges in unpatched Windows systems.

"[The attacker] can run arbitrary code in the context of local system, which pretty much means they own the box ... that one's a particularly nasty one," said Chris Goettl, director of product management at Ivanti, based in South Jordan, Utah.

The vulnerability requires local access to a system, but the public availability of the code increased the risk. An attacker used the code to send targeted spam that, if successful, implemented a two-stage backdoor on a system.

"Once enough public information gets out, it may only be a very short period of time before an attack could be created," Goettl said. "Get the Windows OS updates deployed as quickly as possible on this one."

Microsoft addresses three more public disclosures

Administrators should prioritize patching three more public disclosures highlighted in September Patch Tuesday.

Microsoft resolved a denial-of-service vulnerability (CVE-2018-8409) with ASP.NET Core applications. An attacker could cause a denial of service with a specially crafted request to the application. Microsoft fixed the framework's web request handling abilities, but developers also must build the update into the vulnerable application in .NET Core and ASP.NET Core.

Chris Goettl

A remote code execution vulnerability (CVE-2018-8457) in the Microsoft Scripting Engine opens the door to a phishing attack, where an attacker uses a specially crafted image file to compromise a system and execute arbitrary code. A user could also trigger the attack if they open a specially constructed Office document.

"Phishing is not a true barrier; it's more of a statistical challenge," Goettl said. "If I get enough people targeted, somebody's going to open it."

This exploit is rated critical for Windows desktop systems using Internet Explorer 11 or Microsoft Edge. Organizations that practice least privilege principles can mitigate the impact of this exploit.

Another critical remote code execution vulnerability in Windows (CVE-2018-8475) allows an attacker to send a specially crafted image file to a user, who would trigger the exploit if they open the file.