CVE-2021-39837

Code execution via AcroForm deleteItemAt use-after-free

Published Sep 29, 2021 · Updated Sep 16, 2024

Use-after-free in Adobe Acrobat Reader 2017, 2020, and DC allows local users to execute arbitrary code through a malicious PDF. The AcroForm deleteItemAt action accesses an object after its memory has been freed while processing attacker-controlled form content. Exploitation requires the current user to open the crafted file, after which code runs with that user's privileges.

CVSS severity7.8
High
EPSS probability65.25%
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 Adobe Acrobat Reader 2017, 2020, and DC allows local users to execute arbitrary code through a malicious PDF. The AcroForm deleteItemAt action accesses an object after its memory has been freed while processing attacker-controlled form content. Exploitation requires the current user to open the crafted file, after which code runs with that user's privileges.

The record

CVE
CVE-2021-39837
Published
Sep 29, 2021
Updated
Sep 16, 2024
Vendor
Adobe
Product
Adobe Acrobat Reader
Classifications
CWE-416, T1203, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 29, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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=unspecified <=17.0-Classic 2021 July
  2. Affected versionversion=unspecified <=20.0-Classic 2021 July
  3. Affected versionversion=unspecified <=DC 2021 July
  4. Affected versionversion=unspecified <=None

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Adobe · Adobe Acrobat Readerversion=unspecified <=17.0-Classic 2021 July; version=unspecified <=20.0-Classic 2021 July; version=unspecified <=DC 2021 July; version=unspecified <=None

Published CVSS scores

7.8AdobeCVSS:3.0/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 exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1203Exploitation for Client Execution
T1204.002User Execution: Malicious 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.

Technologies

Your stack

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Your stack

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