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HomeCVEsCVE-2021-26855

CVE-2021-26855

Published: January 27, 2026
Last updated:8 hours ago (January 27, 2026)
Exploit: YesZero-day: YesPatch: YesTrend: Viral
TL;DR
Updated January 27, 2026

CVE-2021-26855 is a critical severity vulnerability with a CVSS score of 9.1. Exploits are available; patches have been released and should be applied urgently. This is classified as a zero-day vulnerability.

Key Points
  • 1Critical severity (CVSS 9.1/10)
  • 2EPSS: 94.00% - very high likelihood of exploitation
  • 3Public exploits are available
  • 4Vendor patches are available
  • 5Strobes Priority Score: 993/1000 (Critical)
  • 6Affects products from: Microsoft
Severity Scores
CVSS v39.1
CVSS v27.5
Priority Score993.0
EPSS Score94.0
Critical
Exploitation LikelihoodCritical
94.00%EPSS

Very high probability of exploitation in the next 30 days

Immediate patching required
94.00%
EPSS
9.1
CVSS
Yes
Exploit
Yes
Patch
Critical Priority
high EPSS • exploit exists • critical severity • high priority

EPSS predicts the probability of exploitation in the next 30 days based on real-world threat data, complementing CVSS severity scores with actual risk assessment.

Description

Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.

CVSS v3 Breakdown
Attack Vector:Network
Attack Complexity:Local
Privileges Required:Network
User Interaction:Network
Scope:Unchanged
Confidentiality:High
Integrity:High
Availability:Network
Exploit References
Exploit-DBExploit-DBCisa.govPacketstormsecurity.comPacketstormsecurity.comPacketstormsecurity.comPacketstormsecurity.comMetasploitMetasploitMetasploit
Patch References
[email protected]Zeroday CZ
Trend Analysis
Viral
Vulnerable Products
VendorProduct
MicrosoftExchange Server
Advisories
CISA: Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.
GitHub AdvisoryNVD
Cite This Page
APA Format
Strobes VI. (2026). CVE-2021-26855 - CVE Details and Analysis. Strobes VI. Retrieved January 27, 2026, from https://vi.strobes.co/cve/CVE-2021-26855
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