Author Archives: Craig Schmugar

Attackers Exploiting WinRAR UNACEV2.DLL Vulnerability (CVE-2018-20250)

Earlier this month Check Point Research reported discovery of a 19 year old code execution vulnerability in the wildly popular WinRAR compression tool. Rarlab reports that that are over 500 million users of this program. While a patched version, 5.70, was released on February 26, attackers are releasing exploits in an effort to reach vulnerable systems before they can be patched.

One recent example piggybacks on a bootlegged copy of Ariana Grande’s hit album “Thank U, Next” with a file name of “Ariana_Grande-thank_u,_next(2019)_[320].rar”

When a vulnerable version of WinRAR is used to extract the contents of this archive, a malicious payload is created in the Startup folder behind the scenes. User Account Control (UAC) does not apply, so no alert is displayed to the user. The next time the system restarts, the malware is run.

Figure 1 – Malformed Archive detected by McAfee as CVE2018-20250!4A63011F5B88
SHA256: e6e5530ed748283d4f6ef3485bfbf84ae573289ad28db0815f711dc45f448bec

Figure 2 – Extracted non-malicious MP3 files

Figure 3 – Extracted Malware payload detected by McAfee as Generic Trojan.i
SHA256: A1C06018B4E331F95A0E33B47F0FAA5CB6A084D15FEC30772923269669F4BC91

In the first week since the vulnerability was disclosed, McAfee has identified over 100 unique exploits and counting, with most of the initial targets residing in the United States at the time of writing.

 

McAfee advises users to keep their anti-malware signatures up to date at all times. McAfee products detect known and unknown malformed ACE files exploiting the vulnerability as CVE2018-20250![Partial hash] starting with the following content

  • V2 DATs version 9183 released March 2, 2019
  • V3 DATs version 3634 released March 2, 2019

Additional GTI coverage exists for email-based attacks, in tandem with the Suspicious Attachment feature. When this feature is enabled, Artemis![Partial hash] detections will occur on known exploits.

Update: An earlier version of this article used the phrase User Access Control (UAC) which has now been changed to User Account Control (UAC) and the term “bypass” which has now been changed to “does not apply.”

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McAfee Protects Against Suspicious Email Attachments

Email remains a top vector for attackers.  Over the years, defenses have evolved, and policy-based protections have become standard for email clients such as Microsoft Outlook and Microsoft Mail.  Such policies are highly effective, but only if they are maintained as attacker’s keep changing their tactics to evade defenses.  For this reason, McAfee endpoint products use a combination of product features and content for increased agility.  In McAfee Endpoint Security (ENS) 10.5+, such protection is enabled via the ‘Detect suspicious email attachments’ option and maintained through DAT content.  This capability goes beyond the level of protection offered by email clients by not only blocking applications and scripts, but also a variety of threat types in their native form, as well as those compressed and contained within archives and other formats.

Figure 1 – ENS 10.6.1 Configuration Screen

An example of this capability in action can be seen against a recent spam run.

In this campaign, a malicious email message contained the attachment BANK DETAILS.ZIP.  Inside this archive was the file BANK DETAILS.ISO.  Malicious ISO spam has been increasing over the past six months, and while it is common for ISO files to be blocked by email clients, this is not the case where the ISO is inside of a ZIP.  Inside the BANK DETAILS.ISO file resides BANK DETAILS.EXE.  Email clients will typically block executable files attached to messages, but not if they are inside a container.

When the email client attempts to write the attachment to disk, ENS scans inside the ZIP and subsequently the contained ISO and EXE files (ZIP -> ISO -> EXE).

Figure 2 – ENS Toaster Popup

In this case, 2-year-old DAT content proactively stopped the threat.

If the system had not been protected, an unsuspecting user might open the ZIP to reveal the ISO.

Figure 3 – Inside ZIP file showing ISO file

The ISO can then be accessed via Windows Explorer, which appears as a DVD Drive containing the executable, password-stealing, payload.

Figure 4 – EXE file inside Bank Details.ISO

Since the advent of policy-based email attachment blocking, attackers have continued to seek ways to evade that protection. ISO abuse may be the latest chapter in the story, but others are sure to follow.

Tens of thousands of new and unique malicious attachments are blocked each month via the ‘Suspicious Attachment’ detection feature.

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