CVE-2021-42321
Actively exploited. CVE-2021-42321 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-17) — exploitation has been observed in the wild, and US federal agencies are required to remediate it under BOD 22-01. Treat patching as urgent.
Public exploit code is available. Proof-of-concept or working exploit code for CVE-2021-42321 is indexed in Metasploit and GitHub PoC. Expect opportunistic scanning and exploitation attempts — prioritize remediation.
An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.
CSIRTS triage
- What
- The vulnerability allows an authenticated attacker to perform remote code execution due to improper validation.
- Who is affected
- Authenticated users of Microsoft Exchange Server are affected.
- Urgency
- Remediation is critical as the vulnerability is actively exploited.
- Action
- Apply the latest security patches for Microsoft Exchange Server.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Exploitation confirmedAlready exploited in the wild (CISA KEV) — the prediction phase is over. Patch now. Riskier than 100% of all EPSS-scored CVEs.
Exploit availability
Public exploit or proof-of-concept code for CVE-2021-42321 is indexed in these free datasets. Available exploit code raises real-world risk independent of the CVSS score.
- MetasploitA Metasploit Framework module targets this CVE — weaponized, point-and-click exploitation.look it up ↗
- GitHub PoCPublic proof-of-concept repositories on GitHub reference this CVE.look it up ↗
Advisory coverage (1)
- criticalexploitedCVE-2021-42321: Microsoft Exchange Server Remote Code Execution Vulnerabilitycisa-kev · 2021-11-17
External references
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[](https://www.csirts.com/cve/CVE-2021-42321)