CVE-2021-31207 Microsoft Exchange Server: dangerous file upload
In plain words: The program accepts files it should refuse, such as programs disguised as ordinary uploads. The attacker can place and run their own tools on the server.
Confirmed exploited by CISA on · US federal patch deadline Nov 17, 2021
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 Security Feature Bypass Vulnerability
- Product
- Microsoft Exchange Server
- CISA description
- Microsoft Exchange Server contains an unspecified vulnerability that allows for security feature bypass.
- Type of flaw
- Dangerous file upload (CWE-20, CWE-434)
- Confirmed exploited
- Nov 3, 2021 — known to be used in ransomware attacks
- US federal patch deadline
- Nov 17, 2021
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Answering about CVE-2021-31207 ·
Questions about CVE-2021-31207
Is CVE-2021-31207 being exploited?
Yes. CISA added CVE-2021-31207 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-2021-31207?
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-2021-31207?
Only if you use Microsoft Exchange Server. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.