---
id: "CVE-2021-26411"
kind: "vulnerability"
aliases: ["CVE-2021-26411"]
title: "Microsoft Internet Explorer: Microsoft Internet Explorer Memory Corruption Vulnerability"
severity: "high"
cvss: 8.8
epss: 0.81667
exploited: true
status: "open"
category: "runtime"
products: [{"name": "Microsoft Internet Explorer", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "internet-explorer", "ransomware", "runtime", "windows"]
not_affected_if: ["no-ie-installed"]
published_at: "2021-03-11T16:15:13+00:00"
first_seen_at: "2026-10-23T19:11:53+00:00"
updated_at: "2026-10-23T21:57:34+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-26411", "first_seen_at": "2026-10-23T19:11:53+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-26411", "first_seen_at": "2026-10-23T19:13:43+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-26411", "first_seen_at": "2026-10-23T21:57:34+00:00"}]
---

# Microsoft Internet Explorer: Microsoft Internet Explorer Memory Corruption Vulnerability

Microsoft Internet Explorer has a memory corruption flaw that attackers have used in real attacks, and CISA lists it as known exploited. A successful exploit can let an attacker run code on the victim's machine.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Microsoft Internet Explorer affected ? fixed ?

## How to check

Run 'reg query "HKLM\SOFTWARE\Microsoft\Internet Explorer" /v svcVersion' or check Internet Explorer's version under Help > About; unknown for other checks.

## Fix

Apply the Microsoft security update for CVE-2021-26411 per vendor instructions; unknown for the exact KB number in these sources.

## Timeline

- 2026-10-23T19:11:53+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-26411
- 2026-10-23T19:13:43+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-26411
- 2026-10-23T21:57:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-26411

## From the sources

Microsoft Internet Explorer contains an unspecified vulnerability that allows for memory corruption.

CISA required action: Apply updates per vendor instructions.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_