CVE-2021-21870Public exploitNetwork attack vector

Code execution via freed FileAttachment annotation

Published Aug 5, 2021 · Updated Aug 3, 2024

Use-after-free in Foxit PDF Reader 10.1.4.37651 allows remote attackers to execute arbitrary code through a crafted PDF. A FileAttachment annotation opens a blocking file chooser after a page switch queues a close handler; that handler destroys the annotation, but creation later resumes and dereferences its freed backing object. Exploitation requires the user to open the document or visit a malicious site with the browser plugin enabled, enabling code execution in the reader process.

CVSS severity8.8
High
EPSS probability1.90%
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 Foxit PDF Reader 10.1.4.37651 allows remote attackers to execute arbitrary code through a crafted PDF. A FileAttachment annotation opens a blocking file chooser after a page switch queues a close handler; that handler destroys the annotation, but creation later resumes and dereferences its freed backing object. Exploitation requires the user to open the document or visit a malicious site with the browser plugin enabled, enabling code execution in the reader process.

The record

CVE
CVE-2021-21870
Published
Aug 5, 2021
Updated
Aug 3, 2024
Vendor
Foxit Software
Product
Foxit PDF Reader
Classifications
CWE-416, T1204.002, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 5, 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

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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 10.1.4.37651

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Foxit Software · Foxit PDF Readerversion=Foxit Reader 10.1.4.37651

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
8.8Cisco TalosCVSS:3.0/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

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
T1204.002User Execution: Malicious File
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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