CVE-2021-42321

Microsoft Exchange: Server Remote Code Execution

As of , CVE-2021-42321 in Microsoft Exchange is on CISA's list of exploited vulnerabilities: CISA listed it on . Our patch-first group: Patch this week.

Exploited
Yes: CISA listed it on 17 November 2021
US federal deadline
1 December 202114 days after CISA listed it. US federal civilian agencies must fix it by then.
Used in ransomware campaigns
Known
EPSS score
0.92Higher than 99% of the CVEs EPSS scores. EPSS estimates the chance of exploitation activity in the next 30 days.
EPSS when listed
Not availableCISA listed it before 4 February 2022, where the EPSS files we read begin.
Public exploit
1 Metasploit module
Fix
No vendor link in CISA's entry

What CISA says to do

Apply updates per vendor instructions.

CISA's required action

What the flaw is

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

CISA's description

Microsoft Exchange Server Remote Code Execution Vulnerability

The CVE record's description, from microsoft

CVE published
10 November 2021
Assigned by
microsoft
CVSS
8.8 High (CVSS 3.1, from the CNA)
CWE-184
Incomplete List of Disallowed Inputs
CWE-502
Deserialization of Untrusted Data
CISA SSVC, exploitation
active
CISA SSVC, automatable
no
CISA SSVC, technical impact
total

Timeline

  1. The CVE record was published.
  2. CISA added it to its list of exploited vulnerabilities.
  3. The US federal deadline to fix it.

Public exploits

Facts from Metasploit's module list and Exploit-DB's index; we never copy exploit code.

  • Metasploit: Microsoft Exchange Server ChainedSerializationBinder RCEexploit module, rank excellent

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