Exploited vulnerability · CISA KEV
Is CVE-2021-27085 exploited? Yes: in CISA KEV since 3 Nov 2021
Gociux · Microsoft Internet Explorer · data: CISA KEV, CVE record, FIRST EPSS
Yes. CVE-2021-27085, Microsoft Internet Explorer Remote Code Execution Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 3 Nov 2021, 237 days after it was published. It affects Microsoft Internet Explorer. If you run it, CISA's required action is: Apply updates per vendor instructions.
exploitedYesCISA KEV · 3 Nov 2021
ransomwareNot knownno confirmed use
EPSStop 10%more likely than most to be exploited
severity8.8CVSS 3.1 · high
US federal due17 Nov 2021BOD 22-01 deadline
What it is
Microsoft Internet Explorer contains an unspecified vulnerability that allows for remote code execution.
| Vendor | Microsoft (391 exploited CVEs in KEV) |
| Product | Internet Explorer |
| Vulnerability | Microsoft Internet Explorer Remote Code Execution Vulnerability |
| Weakness | not specified |
| Published | 11 Mar 2021 |
| Added to KEV | 3 Nov 2021 |
| Reported by (CNA) | microsoft |
What to do
- Check whether you run it. Look for Internet Explorer in your asset inventory, including appliances and cloud images. Stack check lists every exploited Microsoft CVE at once.
- Apply the fix. Apply updates per vendor instructions.
- If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 11 Mar 2021.
- Get told next time. Email alerts when CISA adds a CVE for Microsoft.
Other exploited CVEs in Internet Explorer
- CVE-2010-0249: Microsoft Internet Explorer Use-After-Free Vulnerability (20 May 2026)
- CVE-2010-0806: Microsoft Internet Explorer Use-After-Free Vulnerability (20 May 2026)
- CVE-2010-3962: Microsoft Internet Explorer Uninitialized Memory Corruption Vulnerability (6 Oct 2025)
- CVE-2013-3893: Microsoft Internet Explorer Resource Management Errors Vulnerability (12 Aug 2025)
- CVE-2012-4792: Microsoft Internet Explorer Use-After-Free Vulnerability (23 Jul 2024)
- CVE-2013-3163: Microsoft Internet Explorer Memory Corruption Vulnerability (30 Mar 2023)
References
Questions
Is CVE-2021-27085 being exploited?
Yes. CISA added CVE-2021-27085 to the Known Exploited Vulnerabilities catalog on 3 Nov 2021, which means there is reliable evidence of exploitation in the wild.
Is CVE-2021-27085 used in ransomware attacks?
CISA does not list known ransomware use for it. That can change, and exploitation alone is reason to fix it first.
How do I fix CVE-2021-27085?
Apply updates per vendor instructions. Check Microsoft's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected Internet Explorer and watch it for signs of compromise.
Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in November 2021 · Microsoft scorecard · act-now radar.
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