vulntracker.iovulntracker.io
© 2026 vulntracker.io

CVE-2021-42321

Microsoft Exchange Server Remote Code Execution Vulnerability

HIGH
8.8
CVSS Score
Published: November 10, 2021 at 12:47 AM UTC
Updated: August 19, 2026 at 07:35 PM UTC
1 product affected across 1 vendorExchange Server

Using Microsoft Exchange Server 2016 Cumulative Update 21 by Microsoft?

Get instant alerts when new vulnerabilities affect Microsoft Exchange Server 2016 Cumulative Update 21 - before attackers find them.

Real-time alertsTrack your software stackFree plan available
Start FreeSign In
Severity
HIGH8.8
Exploitation
CISA KEV
Exploit prediction
EPSS 92%
SSVC
Active

Actively Exploited

CISA Known Exploited Vulnerabilities (KEV) Catalog

EPSS Score91.7%

EPSS (Exploit Prediction Scoring System) estimates a 91.7% chance this CVE is exploited in the wild within the next 30 days — higher than 100% of all CVEs. It complements CVSS: a high EPSS on a mid-severity CVE can still be urgent.

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

Required Action
Apply updates per vendor instructions.
Ransomware Use
Known
Added to KEV
Nov 17, 2021
Remediation Due
Dec 1, 2021
1796 days overdue
Notes
https://nvd.nist.gov/vuln/detail/CVE-2021-42321

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Exchange Server· Microsoft
95%
15.0.0 ≤ v < 15.01.2375.01715.01.0 ≤ v < 15.01.2308.02015.02.0 ≤ v < 15.02.0792.01915.02.0 ≤ v < 15.02.0986.01415.0.015.01.015.02.02016 cumulative_update_212016 cumulative_update_222019 cumulative_update_102019 cumulative_update_11
Affected range stops below 15.01.2308.020, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.01.2375.017, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.02.0792.019, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.02.0986.014, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (5)

ExploitThird Party AdvisoryVDB Entry
Source: [email protected]
http://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html
ExploitThird Party AdvisoryVDB Entry
Source: [email protected]
http://packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.html
PatchVendor Advisory
Source: [email protected]
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321
Vendor AdvisoryPatch
Source: cverecord
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321
US Government Resource
Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321

SSVC — Action Prioritization

SSVCActiveNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

8.8HIGHmicrosoft
Vector?

Quick Info

StatusANALYZED
CWE
NVD-CWE-Other

Get alerted

Stop reading CVE feeds looking for your own stack

Track the products you run and VulnTracker tells you when a new CVE affects them — with what is known about fixing it, and nothing about the rest.

Create accountSign in
Free plan, no card