CVE-2021-40420Public exploitNetwork attack vector

Code execution via freed OnBlur object reuse

Published Feb 4, 2022 · Updated Apr 15, 2025

Use-after-free in the JavaScript engine of Foxit PDF Reader 11.1.0.52543 allows remote attackers to execute code via a crafted PDF. The OnBlur handler retains an object pointer while embedded JavaScript calls deletePages(), freeing the object before the handler dereferences it for a virtual call. Exploitation requires the user to open the file, or to visit a malicious site with the browser plugin enabled, and can run attacker-controlled code in the reader's process.

CVSS severity8.8
High
EPSS probability4.69%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in the JavaScript engine of Foxit PDF Reader 11.1.0.52543 allows remote attackers to execute code via a crafted PDF. The OnBlur handler retains an object pointer while embedded JavaScript calls deletePages(), freeing the object before the handler dereferences it for a virtual call. Exploitation requires the user to open the file, or to visit a malicious site with the browser plugin enabled, and can run attacker-controlled code in the reader's process.

The record

CVE
CVE-2021-40420
Published
Feb 4, 2022
Updated
Apr 15, 2025
Vendor
Foxit Software
Product
Foxit PDF Reader
Classifications
CWE-416, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 4, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 15, 2025Record 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=Foxit Reader 11.1.0.52543

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Foxit Software · Foxit PDF Readerversion=Foxit Reader 11.1.0.52543

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
8.8TalosCVSS:3.0/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 exploitationUnconfirmed
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.

Technologies

Your stack

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Your stack

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