CVE-2021-42321 Microsoft Exchange: unsafe data loading
In plain words: The program unpacks saved data from outside without checking it is safe. Usually lets an attacker run code on the server.
Confirmed exploited by CISA on · US federal patch deadline Dec 1, 2021
What to do
- Install Microsoft's security update for Exchange. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Keep a list of every internet-facing server you run so nothing is forgotten.
- Patch anything in this catalog first, ahead of normal patch cycles.
- Put admin and file-transfer apps behind a VPN or single sign-on instead of the open internet.
Who is affected
Work IT. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.
What's at risk: Mass data theft and ransomware: a single flaw in a file-transfer or email server has exposed thousands of organisations at once.
The details
- Official name
- Microsoft Exchange Server Remote Code Execution Vulnerability
- Product
- Microsoft Exchange
- CISA description
- An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.
- Type of flaw
- Unsafe data loading (CWE-184, CWE-502)
- Confirmed exploited
- Nov 17, 2021 — known to be used in ransomware attacks
- US federal patch deadline
- Dec 1, 2021
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Answering about CVE-2021-42321 ·
Questions about CVE-2021-42321
Is CVE-2021-42321 being exploited?
Yes. CISA added CVE-2021-42321 to its Known Exploited Vulnerabilities catalog on Nov 17, 2021, which means there is reliable evidence of real-world attacks, including by ransomware groups.
How do I fix CVE-2021-42321?
Install Microsoft's security update for Exchange. If no update exists, follow the vendor's workaround or stop using the product until one ships. Keep a list of every internet-facing server you run so nothing is forgotten.
Am I affected by CVE-2021-42321?
Only if you use Microsoft Exchange. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.