CVE-2021-42321: Microsoft Exchange Server Remote Code Execution Vulnerability
Vulnerability summary
CVE-2021-42321 is a high (CVSS 8.8) vulnerability in Microsoft Exchange. It is known to be exploited: CISA lists it, first on 17-11-2021. It has been used in ransomware campaigns. EPSS estimates a 91.74% chance of exploitation in the next 30 days, higher than 99.8% of scored vulnerabilities. 3 public exploits are recorded.
Timeline
- 10-11-2021PublishedVulnerability first disclosed.
- 17-11-2021Added to CISA KEVMicrosoft Exchange Server Remote Code Execution Vulnerability
- 01-12-2021CISA remediation dueApply updates per vendor instructions.
- 19-08-2026Last modifiedVulnerability information updated.
Description
Microsoft Exchange Server Remote Code Execution Vulnerability
CVSS metrics
3 scores · 2 sources · 2 versions- NVDNIST8.8HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS trend
Probability
91.74%
Chance of exploitation in the next 30 days
Percentile
100%
Versus all other CVEs
30-day change
0.00 pp
From 91.74% on 20-09-2026
Known exploited
Compare KEV catalogs
CISA KEVListed- Added
- 17-11-2021
- Federal due date
- 01-12-2021
CISA required action
Apply updates per vendor instructions. nvd.nist.gov/vuln/detail/CVE-2021-42321
Public exploits
3 foundExploit Reference (packetstormsecurity.com)
Maturity: unknown
Exploit Reference (packetstormsecurity.com)
Maturity: unknown
Microsoft Exchange Server ChainedSerializationBinder RCE
exploit/windows/http/exchange_chainedserializationbinder_rce
Maturity: weaponized
Weaknesses
CWE · root causeNo weakness data has been published for this record.
Affected systems
Microsoft5 products
- exchange_server2016:cumulative_update_21 | 2016:cumulative_update_22 | 2019:cumulative_update_10 | 2019:cumulative_update_11
- microsoft exchange server 2016 cumulative update 21≥ 15.01.0, < 15.01.2308.020
- microsoft exchange server 2016 cumulative update 22≥ 15.0.0, < 15.01.2375.017
- microsoft exchange server 2019 cumulative update 10≥ 15.02.0, < 15.02.0792.019
- microsoft exchange server 2019 cumulative update 11≥ 15.02.0, < 15.02.0986.014
1 vendor · 5 products
References
5 links
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321X Refsource MISCX TransferredPatchVendor Advisory
- packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.htmlX Refsource MISCX TransferredExploitThird Party AdvisoryVDB Entry
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321Government ResourceUS Government Resource