Flash Exploit, CVE-2018-4878, Spotted in The Wild as Part of Massive Malspam Campaign

Posted by Michael Gorelik on February 25, 2018 at 7:42 PM
Michael Gorelik
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flash-CVE-2018-4878-malspam.jpg 

On February 22, 2018, Morphisec Labs spotted several malicious word documents exploiting the latest Flash vulnerability CVE-2018-4878 in the wild in a massive malspam campaign. Adobe released a patch early February, but it will take some companies weeks, months or even years to rollout the patch and cyber criminals keep developing new ways to exploit the vulnerability in this window

All the documents showed a very low detection ratio on VirusTotal and the next stage artifacts were successfully downloaded from a newly registered domain in all cases. Analyzing the attack, it is clear that it took the attackers only a few easy changes to the original targeted attack to outplay static defenses once more.   

Note to Morphisec customers: Morphisec prevents all variants of this attack, starting from the first version one and half years ago to this latest one leveraging CVE-2018-4878.

01-CVE-2018-4878-in-the-wild.png

The documents were downloaded from the safe-storge[.]biz domain and went almost entirely undetected with an 1/67 detection ratio. 

 02-CVE-2018-4878-in-the-wild-418707-edited.png

While many security defenses missed their goal, the attack did not. In the emails, the victims received short links to the malicious website generated by Google URL Shortener. This gives us the ability to see the analytics for the short links, such as click rate and mail host used. For example, we see that victims opened it through Outlook, Gmail and the Italian webhost Aruba.it. This is of course only a partial picture; we detected five different short links, but there are likely more. 

The analytics for the short links shows the same pattern as legitimate email campaigns. Clickthroughs spike in the first couple of hours after emails are sent. Signature-based defenses, like antiviruses, cannot cope with this pace.  

 shortlink1a.png shortlink2a.png

 shortlink3a.png shortlink4a.png 

shortlink5a.png  Click images to enlarge

After downloading and opening the Word document, the attack exploits the Flash vulnerability 2018-4878 and opens a cmd.exe which is later remotely injected with a malicious shellcode that connects back to the malicious domain.

 03-CVE-2018-4878-in-the-wild.png 

In the next step, the shellcode downloads a "m.db" dll from the same domain, which is executed using regsvr32 process in order to be able to bypass whitelisting solutions:

m.db.png

 Regsvr32 Process:

regsvr32.png

Also the extracted SWF Flash file had very low detection score on VirusTotal:

 04-CVE-2018-4878-in-the-wild.png

 

The disassembled Flash file had a very similar signature to existing PoCs, especially to the stripped 32 bit PoC. Unlike the original attack, however, the current malspam campaign doesn't have a 64 bit implementation.

05-CVE-2018-4878-in-the-wild-032891-edited.png

Conclusion

As expected and predicted, adversaries have quickly adopted the Flash exploit, which is easily reproducible. With small variations to the attack, they successfully launched a massive malspam campaign and bypassed most of the existing static scanning solutions once again.  

Morphisec's Endpoint Threat Prevention solution is agnostic to the morphing and obfuscation of the exploit, and prevented the exploit before any damage could occur.

Artifacts: 

Artifact

Sha2

2018_017581961.docx

6374349443708c96ad41b3f9b891b33f7dec65fdf13e6b424d4d0ab7969c5e71

activeX.bin

eaf0f57cbcbda0dbd2c60c5719731ddeab76b6a10367d2679854202fdca27388

activeX.bin

176ad6129ece312f128a3195bf5afc130801f2e849f89bc97610c1ce8d730772

SWF

6f2c41e665aab873d213583697d70ee79ad59a2b649164c15bd63518b09c429d

<unknown name>.docx

862c6ef1d24d2cba9878b5e919683629c3516d9121f5cf703ff1ca42e2a06a77

Domain: safe-storage[.]biz:443

Short Links:

goo[.]gl/okCYMJ

goo[.]gl/4rHQkh

goo[.]gl/GA8sBY

goo[.]gl/H1EHRG

goo[.]gl/JnYb7s

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Topics: Exploits, Cyber Attacks, Attack Analysis, Malspam

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