What We Do
How we do it
Our Threat Response Unit (TRU) publishes security advisories, blogs, reports, industry publications and webinars based on its original research and the insights driven through proactive threat hunts.
View Threat Intelligence Resources →
Aug 17, 2022
Increase in Observations of Socgholish Malware
THE THREAT Starting in early August 2022 and continuing through the month, eSentire identified a significant increase in Socgholish (aka. FakeUpdates) malware incidents. Socgholish is a loader type…
Read More
View all Advisories →
About Us
eSentire is The Authority in Managed Detection and Response Services, protecting the critical data and applications of 1500+ organizations in 80+ countries from known and unknown cyber threats. Founded in 2001, the company’s mission is to hunt, investigate and stop cyber threats before they become business disrupting events.
Read about how we got here
Leadership Work at eSentire
Sep 20, 2022
eSentire Recognized as Top Global MDR Provider by MSSP Alert, CrowdStrike and G2
Waterloo, ON - September 21, 2022 – eSentire, Inc., the Authority in Managed Detection and Response (MDR), celebrated multiple industry recognitions as the leading global MDR provider, over the last week: Named #9, and the top pure play MDR provider on MSSP Alert’s Top 250 MSSPs global rankingRecognized as the CrowdStrike 2022 Global MSSP Partner of the Year Earned G2’s industry-renowned status…
Read More
e3 Ecosystem
We provide sophisticated cybersecurity solutions for Managed Security Service Providers (MSSPs), Managed Service Providers (MSPs), and Value-Added Resellers (VARs). Find out why you should partner with eSentire, the Authority in Managed Detection and Response, today.
Learn more
Apply to become an e3 ecosystem partner with eSentire, the Authority in Managed Detection and Response.
Login to the Partner Portal for resources and content for current partners.
Security advisories — Nov 22, 2021

Microsoft Exchange Vulnerability - CVE-2021-42321

1 minute read
Speak With A Security Expert Now


eSentire has identified publicly available Proof-of-Concept (PoC) exploit code, for the critical Microsoft Exchange vulnerability CVE-2021-42321. CVE-2021-42321 was announced as part of Microsoft’s November Patch Tuesday release. Exploitation would allow a remote threat actor, with previous authentication, to execute code on vulnerable servers.

Prior to the patch release, Microsoft confirmed that limited exploitation of CVE-2021-42321 had occurred. The release of PoC exploit code significantly increases the likelihood of widespread exploitation in the near future. Organizations that have not already applied the relevant security patches are recommended to do so immediately.

What we’re doing about it

What you should do about it

Additional information

At the time of this reporting, Microsoft has not shared details relating to the real-world exploitation of CVE-2021-42321. Based on limited public details, it appears that only a small number of attacks have occurred. All attacks to date are believed to have been performed by the same threat actor.

The release of PoC exploit code drastically increases the likelihood that multiple threat actor groups will adopt the exploit and use it in attacks in the near future. Additionally, technical details for CVE-2021-42321 have been released. eSentire has not observed exploitation at this time. It should be noted that in order for an attacker to successfully exploit this vulnerability, they would need to have gained prior authentication via a separate attack/vulnerability.

Impacted Products:


  1. https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321
  2. https://techcommunity.microsoft.com/t5/exchange-team-blog/released-november-2021-exchange-server-security-updates/ba-p/2933169
  3. https://peterjson.medium.com/some-notes-about-microsoft-exchange-deserialization-rce-cve-2021-42321-110d04e8852

Join 100,000+ Security Leaders

Get notified when there's a new security advisory, and receive the latest news, intel and helpful tools & assets. You can unsubscribe anytime.

By clicking the button below I confirm that I have read and agree to the eSentire privacy policy.

View Most Recent Blogs