CVE-2021-26419Public exploitNetwork attack vector

Remote code execution via bytecode generator miscompilation

Published May 11, 2021 · Updated Aug 3, 2024

Memory corruption in Internet Explorer 9 and 11 allows remote attackers to execute code when a user opens crafted web content. The jscript9 bytecode generator's LoadCachedHeapArguments path calls EmitPropStore instead of EmitLocalPropInit, giving generated bytecode improper access to an arguments object and causing an out-of-bounds write. Exploitation requires user interaction, and successful code execution occurs in the current user's security context.

CVSS severity7.5
High
EPSS probability22.77%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in Internet Explorer 9 and 11 allows remote attackers to execute code when a user opens crafted web content. The jscript9 bytecode generator's LoadCachedHeapArguments path calls EmitPropStore instead of EmitLocalPropInit, giving generated bytecode improper access to an arguments object and causing an out-of-bounds write. Exploitation requires user interaction, and successful code execution occurs in the current user's security context.

The record

CVE
CVE-2021-26419
Published
May 11, 2021
Updated
Aug 3, 2024
Vendor
Microsoft
Product
Internet Explorer
Classifications
CWE-787, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=1.0.0 <10.0.10240.18931
  2. Affected versionversion=1.0.0 <10.0.14393.4401
  3. Affected versionversion=1.0.0 <10.0.17134.2207
  4. Affected versionversion=1.0.0 <10.0.17763.1935
  5. Affected versionversion=1.0.0 <10.0.18363.1556
  6. Affected versionversion=1.0.0 <10.0.19041.982
  7. Affected versionversion=1.0.0 <6.0
  8. Affected versionversion=1.0.0 <6.0.6003.21117
  9. Affected versionversion=1.0.0 <6.1
  10. Affected versionversion=1.0.0 <6.1.7601.24597
  11. Affected versionversion=1.0.0 <6.2
  12. Affected versionversion=1.0.0 <6.2.9200.23347
  13. Affected versionversion=1.0.0 <6.3.9600.20016
  14. Affected versionversion=1.0.0 <6.3.9600.20017

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Internet Explorerversion=1.0.0 <10.0.10240.18931; version=1.0.0 <10.0.14393.4401; version=1.0.0 <10.0.17134.2207; version=1.0.0 <10.0.17763.1935; version=1.0.0 <10.0.18363.1556; version=1.0.0 <10.0.19041.982; version=1.0.0 <6.0; version=1.0.0 <6.0.6003.21117; version=1.0.0 <6.1; version=1.0.0 <6.1.7601.24597; version=1.0.0 <6.2; version=1.0.0 <6.2.9200.23347; version=1.0.0 <6.3.9600.20016; version=1.0.0 <6.3.9600.20017

Published CVSS scores

7.5Microsoft CorporationCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
7.6NISTAV:N/AC:H/Au:N/C:C/I:C/A:C

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 exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

Public exploit references

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

Technologies

Your stack

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Your stack

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