Is CVE-2021-26857 actively exploited?

Yes. CVE-2021-26857 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, which means exploitation in the wild has been confirmed.

Can CVE-2021-26857 be exploited remotely?

The attack vector of CVE-2021-26857 has not been classified yet.

What is the CVSS score of CVE-2021-26857?

CVE-2021-26857 has not received a CVSS score yet.

HOME VULNERABILITIESCVE-2021-26857

HIGHCISA KEVIN THE WILD

CVE-2021-26857

Published: November 3, 2021

EPSS:38.15%probability of exploitation in 30 daysPercentile:97.1th

Official Description

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

NVD Source

CISA KEV Advisory

Microsoft Exchange Server Remote Code Execution Vulnerability

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

Added to KEV: 2021-11-03Federal patch deadline: 2022-05-03⚠ USED IN RANSOMWARE CAMPAIGNS

Required Action (CISA)

Apply updates per vendor instructions.

Risk Analysis

This vulnerability in Microsoft Exchange Server allows an attacker to execute arbitrary code remotely. Its inclusion in the ProxyLogon exploit chain and confirmed exploitation by CISA (is_in_kev: true) indicate its critical urgency. The high EPSS score of 0.38152 further suggests a significant likelihood of exploitation.

This vulnerability is actively being exploited in the wild and is part of the CISA Known Exploited Vulnerabilities Catalog. Given its nature as a remote code execution flaw in Exchange Server, it is likely remotely exploitable.

Recommended Action

Apply the latest security updates for Microsoft Exchange Server to patch this vulnerability. Ensure all Exchange servers are properly configured and exposed services are minimized.

Generated by the CTIWATCH analysis pipeline from this CVE's metadata (CVSS, EPSS, KEV status, exploit intelligence). Verify against vendor advisories before acting.

Technical Analysis

CVE-2021-26857 requires local access, meaning attackers must already have a foothold on the target system.

Exploitation requires some privileges, which limits the exposure to scenarios where an attacker has already gained initial access.

CISA has added CVE-2021-26857 to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. U.S. federal agencies are required to patch this within the mandated timeframe, and all organizations should treat remediation as urgent.