CVE-2021-26857

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

Browse: All 2021 CVEs · All vendors

CISA KEV
Yes — actively exploited (added 2021-11-03, remediation due 2022-05-03)
Ransomware
Known ransomware campaign use
Weakness (CWE)
CWE-502

Description

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

Affected products

Affected ranges per NVD CPE data; confirm exact versions in the vendor advisory.

Required action (CISA)

Apply updates per vendor instructions. Federal remediation deadline: 2022-05-03.

How to prioritize this

This vulnerability is on the CISA KEV list, meaning it is being actively exploited — treat it as urgent regardless of the raw CVSS number. Use the live CVE lookup for the latest NVD data, and the CVSS 3.1 calculator to model your own environmental score.

FAQ

Is CVE-2021-26857 actively exploited?

Yes. CISA added CVE-2021-26857 to its Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03, with a federal remediation deadline of 2022-05-03. A KEV listing means real-world exploitation is confirmed, so patching this should be prioritized above many higher-CVSS bugs that aren't being exploited.

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

CVE-2021-26857 has no published CVSS base score yet — NVD analysis can lag disclosure. Check the vendor references for an interim severity.

Related vulnerabilities

Data source: NVD & CISA KEV. Shown as-is; nothing added. Last generated from NVD data — re-check the live tool for updates.