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Security advisories | Feb 05, 2021

Chrome and Internet Explorer Zero-Day Vulnerabilities

THE THREAT

On February 4th, 2021, two separate zero-day vulnerabilities impacting the Chrome and Internet Explorer web browsers were announced.

Google confirmed a high severity vulnerability in Google Chrome that is tracked as CVE-2021-21148. The vulnerability is classified as Heap Buffer Overflow. While Google has stated there are reports of exploitation in the wild, no additional details have been provided at this time.

The South Korean cyber-security company ENKI confirmed the existence of a zero-day vulnerability affecting Internet Explorer 11, after they identified targeted attacks against their employees. The currently unnamed IE vulnerability is classified as a double-free vulnerability and has been exploited to exfiltrate victim information and deliver additional malicious content.

What we’re doing about it

  • MVS has local plugins to identify systems vulnerable to CVE-2021-21148
    • MVS will automatically add the relevant checks for the Internet Explorer zero-day vulnerability once details are made available
    • MVS customers seeking assistance with their review or scans, please contact your MVS consultant or the eSentire Security Operations Center (SOC)
  • eSentire security teams continue to track this topic for additional details and detection opportunities

What you should do about it

  • Ensure Chrome browsers are updated to version 88.0.4324.150
  • Consider replacing Internet Explorer with alternative modern browsers such as Microsoft Edge, Mozilla Firefox, or Google Chrome

Additional information

CVE-2021-21148 is a heap buffer overflow vulnerability found in the V8 JavaScript engine used in the Chrome browser. Chrome updates are automatically applied to users but requires that end users close and restart Chrome.

The Internet Explorer zero-day was employed by suspected North Korean state- affiliated actors, in a previously reported campaign, targeting security researchers. The security researchers were targeted via social engineering attacks with malicious MHT/MHTML files. If the files are opened using Internet Explorer (the default application for MHT files), the user is prompted to allow script execution. If permission is given, a JavaScript payload would pull down additional malicious payloads including the IE zero-day exploit.

There is speculation that CVE-2021-21148 was exploited in this campaign. Links between exploitation of CVE-2021-21148 and this campaign have not been verified at this time.

References:

[1] https://chromereleases.googleblog.com/2021/02/stable-channel-update-for-desktop_4.html

[2] https://enki.co.kr/blog/2021/02/04/ie_0day.html

[3] https://blog.google/threat-analysis-group/new-campaign-targeting-security-researchers/