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VulnerabilityCVE-2021-26411Published 2021-03-11

CVE-2021-26411 — Microsoft Internet Explorer 11

highCISA KEVRansomwarePublic exploit2 PoC repos

As of 2026-11-07, CVE-2021-26411 is a HIGH-severity vulnerability in Microsoft Internet Explorer 11, CVSS v3.1 8.8, EPSS 81.6% (99.6th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), with a US federal remediation deadline of 2021-11-17, and CISA links it to known ransomware campaigns. Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2021-26411, most recently “Exploit kits remain active in April 2021: RIG, Spelevo, PurpleFox, Underminer, Bottle, Magnitude targeting Internet Explorer (CVE-2020-0674, CVE-2021-26411, CVE-2018-8174, CVE-2018-15982, CVE-2020-1380)”.

CVSS v3.1
8.8/10High
EPSS
81.6%Higher than 99.6% of scored CVEs
CISA KEV
ListedAdded · due 2021-11-17
Tracked threats
1Campaigns referencing it
Priority
10/10Threadlinqs triage score
Published
Updated 2026-10-01
CVSS v3.1 8.8 (HIGH) · EPSS 81.6% (higher than 99.6% of all scored CVEs) · Priority 10/10 · Published 2021-03-11

Last updated:

What is CVE-2021-26411?

Internet Explorer Memory Corruption Vulnerability

The record classifies CVE-2021-26411 under weakness class CWE-416. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs a user to take an action first, and has high impact on integrity. 3 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 2067 days ago.

Severity and exploitation probability

CVSS v3.1 base score
8.8 — HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C
EPSS (FIRST)
81.6% probability of exploitation in the next 30 days, higher than 99.6% of all scored CVEs
CISA KEV
Listed since 2021-11-03, federal remediation deadline 2021-11-17 — used in known ransomware campaigns
Threadlinqs priority
10/10 — CISA lists it as used in ransomware, which Threadlinqs scores at the maximum
Published
2021-03-11, last modified 2026-10-01

Is CVE-2021-26411 being exploited?

CISA added CVE-2021-26411 to the Known Exploited Vulnerabilities catalog on 2021-11-03, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2021-11-17 under BOD 22-01. CISA flags the vulnerability as one used in known ransomware campaigns. Weaponised exploit code for CVE-2021-26411 is publicly available. 2 public proof-of-concept repositories are tracked for this identifier. It currently carries a trending score of 48 in the Threadlinqs vulnerability feed.

Affected products and versions

  • Microsoft: Internet Explorer 11, Internet Explorer 9, Edge (EdgeHTML-based)

How to fix CVE-2021-26411

The record marks a vendor fix as available for CVE-2021-26411. Patch reference: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26411. Because CVE-2021-26411 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2021-11-17. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

Threat activity tracking CVE-2021-26411

1 tracked threat in the Threadlinqs corpus references CVE-2021-26411, either in the campaign’s CVE list or as an indicator on the campaign record.

Sources

Enriched from CVE.org, NVD, FIRST EPSS, CISA KEV, public proof-of-concept repositories. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.

Vendor advisory and patch