CVE-2021-42298Known exploitation

SYSTEM code execution via crafted PDF JavaScript

Published Nov 10, 2021 · Updated Aug 19, 2026

Code injection in Microsoft Malware Protection Engine before 1.1.18700.3 allows remote attackers to execute code via a crafted PDF. The PDF's embedded JavaScript exploits an undisclosed flaw in the engine's JavaScript interpreter when Defender automatically scans the downloaded file. A user must visit the delivery URL and download the file; the scan then runs the exploit as SYSTEM, granting full host control.

CVSS severity7.8
High
EPSS probability5.80%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Code injection in Microsoft Malware Protection Engine before 1.1.18700.3 allows remote attackers to execute code via a crafted PDF. The PDF's embedded JavaScript exploits an undisclosed flaw in the engine's JavaScript interpreter when Defender automatically scans the downloaded file. A user must visit the delivery URL and download the file; the scan then runs the exploit as SYSTEM, granting full host control.

The record

CVE
CVE-2021-42298
Published
Nov 10, 2021
Updated
Aug 19, 2026
Vendor
Microsoft
Product
Microsoft Malware Protection Engine
Classifications
CWE-94, T1203, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 10, 2021CVE publishedPublication date reported by the CVE source.
  2. 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=1.1.0.0 <1.1.18700.3

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Malware Protection Engineversion=1.1.0.0 <1.1.18700.3

Published CVSS scores

9.3NVDAV:N/AC:M/Au:N/C:C/I:C/A:C
7.8NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
7.8MicrosoftCVSS:3.1/AV:L/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)
Vectorlocal
Privilegesunauthenticated
Known exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-94Improper Control of Generation of Code ('Code Injection')
T1203Exploitation for Client Execution
T1204.002Malicious File

Public exploit references

No public exploit references are available in this record.

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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