CVE-2021-42321

High (8.8) in Microsoft Exchange. In CISA KEV since 2021-11-17, with known ransomware use. EPSS 92% chance of exploitation in the next 30 days.

EPSS

92% chance of exploitation in the next 30 days; higher than 99% of CVEs (scores of 2026-10-31)

CISA KEV

listed 2021-11-17, due 2021-12-01, known ransomware use

Published

2021-11-10

Modified

2026-08-19

Record from

the NVD, synced 2026-10-19

Affected

• microsoft:exchange_server

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321
• http://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html
• http://packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.html
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321

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