The actively exploited Windows spoofing vulnerability patched last week by Microsoft has been known for more than two years, researchers pointed out.

Microsoft’s August 2020 Patch Tuesday updates addressed 120 vulnerabilities, including an Internet Explorer zero-day that has been chained with a Windows flaw in attacks linked to the threat actor named DarkHotel, and a Windows spoofing issue tracked as CVE-2020-1464.

The tech giant describes CVE-2020-1464 as a spoofing flaw related to Windows incorrectly validating file signatures. An attacker can exploit the vulnerability to bypass security features and load improperly signed files, Microsoft says in its advisory.

Researchers analyzed CVE-2020-1464 after Microsoft released its patch and noticed that it’s likely a vulnerability that has been known for years and which Microsoft has been refusing to fix.

In a blog post published over the weekend, researcher Tal Be’ery explained that the vulnerability, which has been named GlueBall, has been known since August 2018, when a file sample exploiting it was uploaded to VirusTotal.

Microsoft was informed about the issue at the time and details were disclosed on the VirusTotal blog in January 2019, but the vendor decided not to fix it.

“Microsoft Windows keeps the Authenticode signature valid after appending any content to the end of Windows Installer (.MSI) files signed by any software developer. This behaviour can be exploited by attackers to bypass some security solutions that rely on Microsoft Windows code signing to decide if files are trusted. The scenario is especially dangerous when the appended code is a malicious JAR because the resulting file has a valid signature according to Microsoft Windows and the malware can be directly executed by Java,” Bernardo Quintero, founder of VirusTotal, explained in the January 2019 blog post.

Shortly after the blog post was published, several others analyzed the issue and made their findings public. In June 2020, researchers noticed that someone had been exploiting GlueBall to deliver malware, and in August it was finally patched by Microsoft.

“[The] way Microsoft had handled the vulnerability report seems rather strange,” Be’ery noted. “It was very clear to everyone involved, Microsoft included, that GlueBall is indeed a valid vulnerability exploited in the wild. Therefore, it is not clear why it was only patched now and not two years ago.”

SecurityWeek has reached out to Microsoft, but the company has not provided any clarifications regarding its decision not to patch CVE-2020-1464 sooner.

“A security update was released in August. Customers who apply the update, or have automatic updates enabled, will be protected. We continue to encourage customers to turn on automatic updates to help ensure they are protected,” said a Microsoft spokesperson.

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