CVE-2021-26411Known exploitationPublic exploitNetwork attack vector

Remote code execution via stale attribute-array index

Published Mar 11, 2021 · Updated Aug 19, 2026

Use-after-free in MSHTML in Microsoft Internet Explorer and Edge Legacy allows remote attackers to execute code via crafted web content. CElement::ie9_removeAttributeNodeInternal calculates attribute-array indices before a user-controlled callback, then reuses them after clearAttributes changes the backing store, causing a double free. A victim must open the malicious content; successful exploitation supplies an arbitrary memory read-write primitive and code execution in the browser context.

CVSS severity8.8
High
EPSS probability80.77%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in MSHTML in Microsoft Internet Explorer and Edge Legacy allows remote attackers to execute code via crafted web content. CElement::ie9_removeAttributeNodeInternal calculates attribute-array indices before a user-controlled callback, then reuses them after clearAttributes changes the backing store, causing a double free. A victim must open the malicious content; successful exploitation supplies an arbitrary memory read-write primitive and code execution in the browser context.

The record

CVE
CVE-2021-26411
Published
Mar 11, 2021
Updated
Aug 19, 2026
Vendor
Microsoft
Product
Microsoft Edge Legacy
Classifications
CWE-416, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2021Exploitation reportedCISA Known Exploited Vulnerabilities entry
  3. Aug 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.0..0 <10.0.17134.2087

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Edge Legacyversion=1.0..0 <10.0.17134.2087
Microsoft · Internet Explorer 11version=1.0.0 <10.0.17134.2087
Microsoft · Internet Explorer 9version=1.0.0 <6.0.6003.21070

Published CVSS scores

5.1NIST NVDAV:N/AC:H/Au:N/C:P/I:P/A:P
8.8Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L
8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-416Use After Free
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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