CVE-2021-27065 Microsoft Exchange Server: command or code injection
In plain words: The program treats text it receives as instructions instead of plain data. The attacker can run commands on the machine — often the whole device is taken over.
Confirmed exploited by CISA on · US federal patch deadline May 3, 2022
What to do
- Install Microsoft's security update for Exchange Server. 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 Server
- CISA description
- Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.
- Type of flaw
- Command or code injection (CWE-39)
- Confirmed exploited
- Nov 3, 2021 — known to be used in ransomware attacks
- US federal patch deadline
- May 3, 2022
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Answering about CVE-2021-27065 ·
Questions about CVE-2021-27065
Is CVE-2021-27065 being exploited?
Yes. CISA added CVE-2021-27065 to its Known Exploited Vulnerabilities catalog on Nov 3, 2021, which means there is reliable evidence of real-world attacks, including by ransomware groups.
How do I fix CVE-2021-27065?
Install Microsoft's security update for Exchange Server. 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-2021-27065?
Only if you use Microsoft Exchange Server. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.