CVE-2021-42321
Published: November 17, 2021
Official Description
An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.
CISA KEV Advisory
Microsoft Exchange Server Remote Code Execution Vulnerability
An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.
Apply updates per vendor instructions.
Risk Analysis
Microsoft Exchange allows an authenticated attacker to achieve remote code execution through improper validation in cmdlet arguments. This vulnerability poses a significant risk as it allows for arbitrary code execution on the server. Its high EPSS score of 0.93422 and inclusion in CISA's KEV indicate a high likelihood of exploitation.
This vulnerability is actively exploited in the wild. While requiring authentication, the ability to perform remote code execution makes it a critical threat once an attacker gains initial access.
Administrators must apply the latest security updates for Microsoft Exchange to address this vulnerability. Additionally, implement strong authentication policies and monitor for suspicious cmdlet usage.
Technical Analysis
CVE-2021-42321 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-2021-42321 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.
Affected Vendors & Products
Exploit & PoC Resources
All References (1)
Quick Facts
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2021-42321 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
- !CISA KEV: Federal agencies must patch per BOD 22-01 timeline
- !Active exploitation confirmed — treat as P1