CVE-2021-42321KEV · OVERDUE

Microsoft Exchange Server Remote Code Execution Vulnerability

High · published November 10, 2021

Patch now

Confirmed exploited, and the score agrees

CVSS calls it high at 8.8. It is confirmed in active exploitation. It sits in the 99.8th percentile for exploit probability.

1789
days past CISA
deadline
CVSS v3.1
8.8
EPSS
92%
Percentile
99.8
In the wild
Confirmed
What it is

🚨 A sneaky flaw in Microsoft Exchange Server lets attackers execute remote code without breaking a sweat! ⚡ Think of it like a delivery person who can open your front door and rearrange your furniture without ever asking for permission — it’s unnervingly simple! An attacker could exploit this vulnerability to gain complete control over your Exchange Server, putting sensitive emails and data at severe risk. They could not only snoop on communications but also install malicious software that could wreak havoc throughout your network. This is absolutely devastating for any organization!

Put simply

Think of it like a delivery person who can open your front door and rearrange your furniture without ever asking for permission — it’s unnervingly simple! This remote code execution vulnerability arises from improper validation of cmdlets and allows the execution of arbitrary commands on the server without authentication, which means the door is wide open for intruders.

What to do

An attacker could exploit this vulnerability to gain complete control over your Exchange Server, putting sensitive emails and data at severe risk. They could not only snoop on communications but also install malicious software that could wreak havoc throughout your network. This is absolutely devastating for any organization! Immediately apply the security patches provided by Microsoft to fix this vulnerability. Additionally, review your network's security protocols and consider implementing multi-factor authentication to bolster defenses. Don't wait — act fast to secure your system! You've got this! Follow these steps, and you'll be on your way to restoring safety and security to your Exchange Server! 🛡️

The record
Technical detail
CVSS v3.1
8.8 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.91737 · 99.8th percentile
Published
2021-11-10T06:19Z
KEV added
2021-11-17 · due 2021-12-01
Affected products (4)
ProductVersionsFixed in
microsoft/exchange_serverall versions—
microsoft/exchange_serverall versions—
microsoft/exchange_serverall versions—
microsoft/exchange_serverall versions—
References (5)
EPSS history
Timeline
  • 17 NOV 00:00Z
    Added to CISA KEV — remediate by Dec 1
    kev
  • 10 NOV 00:47Z
    Microsoft Exchange Server Remote Code Execution Vulnerability
    cvelistv5