Google: Microsoft Improperly Patched Exploited Windows Vulnerability

Google Project Zero has disclosed a Windows zero-day vulnerability caused by the improper fix for CVE-2020-0986, a security flaw abused in a campaign dubbed Operation PowerFall.

Tracked as CVE-2020-17008, the new vulnerability was reported to Microsoft on September 24. As per Project Zero’s policy, details were made public 90 days later, on December 23, despite the fact that Microsoft missed the patch deadline.

Disclosed in May 2020, CVE-2020-0986 was initially reported to Microsoft in December 2019 and a patch was released in June 2020. Attacks targeting the vulnerability were observed within days after disclosure.

In August 2020, Kaspersky published information on attacks chaining CVE-2020-0986 with a zero-day in Internet Explorer, as part of an attack campaign referred to as Operation PowerFall.

“By using this vulnerability it is possible to manipulate the memory of the splwow64.exe process to achieve execution of arbitrary code in the process and escape the Internet Explorer 11 sandbox because splwow64.exe is running with medium integrity level,” Kaspersky explained in a September post.

Also an elevation of privilege bug in splwow64.exe, CVE-2020-17008 can be abused by simply changing the exploitation method for CVE-2020-0986, an arbitrary pointer dereference flaw affecting the GDI Print/Print Spooler API.

Google Project Zero researcher Maddie Stone explains that CVE-2020-17008 is actually nearly identical to CVE-2020-0986, the only difference being that “for CVE-2020-0986 the attacker sent a pointer and now the attacker sends an offset.”

On Twitter, Stone notes that Microsoft’s fix was faulty because it simply changed the pointers to offsets, failing to prevent an attacker to control “the args to the memcpy.”

The researcher also published proof-of-concept (PoC) code targeting CVE-2020-17008, noting that the exploit is an adaptation of the PoC Kaspersky released for CVE-2020-0986.

“It triggers the memcpy vulnerability twice: first to leak the heap address where the message is stored and what the offset is added to to generate the pointers and then to do the write-what-where,” Stone says.

Project Zero's Maddie Stone on improperly patched vulnerabilities

Microsoft, which acknowledged the issue one day after receiving the vulnerability report, was aiming for the release of a patch in November, but postponed the fix due to issues identified in testing. The company is currently aiming to address the bug in January 2021.

Related: Windows and IE Zero-Day Vulnerabilities Chained in ‘PowerFall’ Attacks

Related: Researchers Divulge Details on Five Windows Zero Days

Related: Sophisticated Threat Actor Exploited Oracle Solaris Zero-Day

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Ionut Arghire is an international correspondent for SecurityWeek.

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