CVE-2021-40444 Microsoft MSHTML: file path flaw
In plain words: The program can be tricked into reading or writing files outside the folder it should stay in. Leaks files such as passwords and settings, or overwrites important ones.
Confirmed exploited by CISA on · US federal patch deadline Nov 17, 2021
What to do
- Install Microsoft's security update for MSHTML. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Let the browser auto-update and relaunch it when it asks — the fix is not active until you do.
- Keep extensions to a minimum and remove ones you do not recognise.
- Stop using Internet Explorer and any browser that no longer gets updates.
Who is affected
Could reach you. Used in ransomware, which spreads to ordinary people and small businesses.
What's at risk: A malicious or hacked website can be enough. Browser bugs are often the first step in a longer attack on the whole computer or phone.
The details
- Official name
- Microsoft MSHTML Remote Code Execution Vulnerability
- Product
- Microsoft MSHTML
- CISA description
- Microsoft MSHTML contains a unspecified vulnerability that allows for remote code execution.
- Type of flaw
- File path flaw (CWE-22)
- 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-2021-40444 ·
Questions about CVE-2021-40444
Is CVE-2021-40444 being exploited?
Yes. CISA added CVE-2021-40444 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-2021-40444?
Install Microsoft's security update for MSHTML. If no update exists, follow the vendor's workaround or stop using the product until one ships. Let the browser auto-update and relaunch it when it asks — the fix is not active until you do.
Am I affected by CVE-2021-40444?
Only if you use Microsoft MSHTML. Used in ransomware, which spreads to ordinary people and small businesses.