Exploited vulnerability · CISA KEV

Is CVE-2021-42321 exploited? Yes: in CISA KEV since 17 Nov 2021

Gociux · Microsoft Exchange · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2021-42321, Microsoft Exchange Server Remote Code Execution Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 17 Nov 2021, 7 days after it was published. It is known to be used in ransomware campaigns. It affects Microsoft Exchange. If you run it, CISA's required action is: Apply updates per vendor instructions.

What it is

An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.

What to do

1. Check whether you run it. Look for Exchange in your asset inventory, including appliances and cloud images. Stack check lists every exploited Microsoft CVE at once.
2. Apply the fix. Apply updates per vendor instructions.
3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 10 Nov 2021.
4. Get told next time. Email alerts when CISA adds a CVE for Microsoft.

References

• nvd.nist.gov/vuln/detail/CVE-2021-42321

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in November 2021 · Microsoft scorecard · act-now radar.