Flash Zero Day (CVE-2018-4878)

A zero day Flash exploit caught targeting South Korean users was announced by South Korea's CERT on January 31, 2018. The exploit was embedded in an Excel spreadsheet.

Upon opening the spreadsheet the Flash file loads a second stage which exploits a "use-after-free" RCE vulnerability (CVE-2018-4878). The embedded payload that is launched is a remote administration tool (RAT) and is encrypted to prevent detection by anti-malware protections. The payload also downloads a decryption key to decrypt the RAT.

Adobe released a patch on February 6, 2018 in bulletin APSB18-03 to address the vulnerability.

The primary attack vector was likely email with the malicious spreadsheet sent out via a targeted spam campaign. Spam filters that can detect malicious spam or a Secure Email Gateway device would help clean these types of emails out before they even get to your end user's inbox. In case malicious emails still make it through your protection controls, it's always important to hold regular security awareness training for your users to help them identify the various social engineering techniques used by spammers.

While all the blogs writing about this CVE provide hashes and IOC's, we don't consider it sufficient to only protect against these specific files. With a public PoC available, there's a good chance that this CVE will make its way into other attacks.

Although the original attack was apparently launched over email, there's no reason why the same attack couldn't be launched via a malicious website. Flash exploits were used quite often in the past in web exploit kits. Secure Web Gateways can help prevent these types of attacks by filtering malicious content out so that it never reaches your user's web browsers.

Our analysis and research into this vulnerability has already been pushed to our security offerings and we stress that "Defense in Depth" is important to prevent these sorts of attacks. Trustwave customers will find detection rules against these vulnerabilities in the following security offerings:

Trustwave Secure Email Gateway (SEG) update AMAX v102
Trustwave Secure Web Gateway (SWG) update SU215
Trustwave UTM update 106 (all updates are automated)

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