CVE-2019-1132 Windows Zero-Day exploited by Buhtrap Group in government attack

The CVE-2019-1132 flaw addressed by Microsoft this month was exploited by Buhtrap threat actor to target a government organization in Eastern Europe.

Microsoft Patch Tuesday updates for July 2019 address a total of 77 vulnerabilities, including two privilege escalation flaws actively exploited in the wild.

The first vulnerability, tracked as CVE-2019-1132, affects the Win32k component and could be exploited to run arbitrary code in kernel mode. The second one, tracked as CVE-2019.0880, affects Windows 7 and Server 2008. The issue resides in the way splwow64 (Thunking Spooler APIs) handles certain calls.

According to experts at ESET, the Windows zero-day flaw CVE-2019-1132 was exploited by the Buhtrap threat actor in a targeted attack aimed at a government organization in Eastern Europe. Experts pointed out that this was the first time Buhtrap had used a zero-day flaw in its operations.

Since August of 2015, the Buhtrap group has conducted 13 successful attacks against financial institutions stealing more than ₽1.86 billion RUB ($27.4M USD). In April 2015, ESET discovered a malware campaign dubbed Operation Buhtrap, a conjunction of the Russian word for accountant “Buhgalter” and the English word “trap”.  So far Buhtrap has not been seen anywhere else in the wild, 88 percent of targets have been in Russia and ten percent in Ukraine.  Analysts have also likened the campaign to the Anunak/Carbanak campaign, which also targeted Russian and Ukrainian Banks.

Back to nowadays, ESET reported the attacks exploiting the CVE-2019-1132 to Microsoft. Buhtrap threat actor developed an exploit that relies on popup menu objects, a technique that was observed in other attacks over the years.

“but June 2019 was the first time we saw the Buhtrap group use a zero-day exploit as part of a campaign. In that case, we observed Buhtrap using a local privilege escalation exploit, CVE-2019-1132, against one of its victims.” reads the analysis published by ESET.

“The exploit abuses a local privilege escalation vulnerability in Microsoft Windows, specifically a NULL pointer dereference in the win32k.sys component. Once the exploit was discovered and analyzed, it was reported to the Microsoft Security Response Center, who promptly fixed the vulnerability and released a patch.“

ESET researchers discovered that the flaw was exploited in an attack aimed at a government institution in Eastern Europe in June. Buhtrap threat actors exploited the flaw to execute malicious code with the highest privileges on the target systems.

Attackers used a weaponized document to deliver a backdoor that also implements info-stealing capabilities through a module called “grabber.”

“The first module, called “grabber” by its author, is a standalone password stealer. It tries to harvest passwords from mail clients, browsers, etc., and sends them to a C&C server.” continues the report. “The second module is something that we have come to expect from Buhtrap operators: an NSIS installer containing a legitimate application that will be abused to side load the Buhtrap main backdoor. The legitimate application that is abused in this case is AVZ, a free anti-virus scanner.”

The group apparently shifted targets, but the real reason it is still unclear.

“While we do not know why this group has suddenly shifted targets, it is a good example of the more and more blurry lines separating pure espionage groups from the ones mostly doing crimeware.” concludes the analysis. “In this case, it is unclear if one or several members of this group decided to change focus and for what reasons, but it is definitely something that we are likely to see more of going forward,”

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Pierluigi Paganini

(SecurityAffairs – CVE-2019-1132, Buhtrap)

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