CVE-2021-26855 Details
This vulnerability is part of an attack chain affecting Microsoft Exchange Server, ultimately resulting in an external unauthenticated attacker gaining remote code execution on the affected Exchange server. The initial attack requires the ability to make an untrusted connection to Exchange server port 443. The CVEs used in this attack chain are CVE-2021-26855 (ProxyLogon), CVE-2021-26857, CVE-2021-26858 and CVE-2021-27065.

This attack chain is being used in the wild to remotely compromise hosts. More information can be found here: <a href="https://www.microsoft.com/security/blog/2021/03/02/hafnium-targeting-exchange-servers/">https://www.microsoft.com/security/blog/2021/03/02/hafnium-targeting-exchange-servers/</a>
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Exploit prediction scoring system (EPSS) score for CVE-2021-26855
EPSS (Exploit Prediction Scoring System): EPSS predicts the likelihood that a vulnerability will be exploited in the wild. A higher percentage means a greater chance of an exploit occurring. The EPSS model produces a probability score between 0 and 1 (0 and 100%).
94.36 Probability of exploitation activity being observed over the next 30 days (100th percentile)
CVSS score for CVE-2021-26855
CVSS (Common Vulnerability Scoring System): An open framework owned and managed by FIRST.Org, Inc. that assigns a numerical score from 0 to 10 to software vulnerabilities to indicate their severity.
9.1 Critical
Products affected by CVE-2021-26855
Exchange Server 2013
Exchange Server 2016
Exchange Server 2019
DVE Score by Bitsight AI
DVE scores complement traditional static scoring systems like CVSS with Bitsight AI powered real-time threat intelligence and underground cyber criminal activity so that security teams can reduce alert fatigue and focus on vulnerabilities most likely to be exploited.
Low
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CVE-2021-26855 Global Footprint

Top 10 Identified Countries

Country Observations Percentage
FR 2,151 25.42%
US 1,081 12.77%
RU 943 11.14%
DE 829 9.80%
GB 293 3.46%
CN 243 2.87%
IT 198 2.34%
HK 161 1.90%
AU 153 1.81%
CA 136 1.61%

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CVE-2021-26855 Industry Footprint

Top 10 Identified Industries

*Service provider organizations (typically Technology and Telecommunications) are disproportionally represented in the results given their upstream ownership of end-user infrastructure. See our FAQs.

Industry* Observations Percentage
Telecommunications 2,256 68.68%
Technology 529 16.10%
Manufacturing 99 3.01%
Government/Politics 62 1.89%
Business Services 60 1.83%
Education 31 0.94%
Transportation 30 0.91%
Healthcare/Wellness 29 0.88%
Finance 27 0.82%
Energy/Resources 23 0.70%

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