CVE-2021-39840
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedAcrobat Reader DC versions 2021.005.20060 (and earlier), 2020.004.30006 (and earlier) and 2017.011.30199 (and earlier) are affected by a use-after-free vulnerability when processing AcroForms that could result in arbitrary code execution in the context of the current user. User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceA use-after-free vulnerability exists in Adobe Acrobat Reader DC when processing AcroForms (interactive PDF forms). The vulnerability allows arbitrary code execution in the context of the current user by exploiting memory that is accessed after being freed during AcroForm processing.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 20.001.30005, <= 20.004.30006>= 17.011.30059, <= 17.011.30199>= 20.001.30005, <= 20.004.30006>= 17.011.30059, <= 17.011.30199>= 15.008.20082, <= 21.005.20058>= 15.008.20082, <= 21.005.20060>= 15.008.20082, <= 21.005.20058>= 15.008.20082, <= 21.005.20060CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check if Adobe Acrobat or Reader is installedOpen Windows Control Panel > Programs and Features, or run 'Get-ItemProperty HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\* | Select-Object DisplayName, DisplayVersion' in PowerShell to list installed Adobe productsAffected if Adobe Acrobat or Adobe Acrobat Reader DC appears in the installed programs list
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Determine the exact installed versionOpen Adobe Acrobat/Reader, go to Help > About Adobe Acrobat Reader, or run the executable with -version flag, or check the version in the Windows registry at HKLM\SOFTWARE\Adobe\Acrobat\Distro\{version}\InstallPathAffected if A version number is returned that can be compared to affected ranges
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Compare version against affected rangesCompare the installed version number to these vulnerable ranges: 20.001.30005 through 20.004.30006; 17.011.30059 through 17.011.30199; 15.008.20082 through 21.005.20058; 15.008.20082 through 21.005.20060Affected if The installed version falls within any of these inclusive ranges
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Verify AcroForms processing capabilityThe vulnerability affects AcroForm processing which is a standard feature in Adobe Acrobat/Reader. Open any PDF and check if forms can be filled or forms toolbar is available under Tools > FormsAffected if AcroForms functionality is present and the version is in the affected range
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Confirm product edition matches affected linesDetermine if the installation is Adobe Acrobat DC, Adobe Acrobat Reader DC, Adobe Acrobat, or Adobe Acrobat Reader by checking the product name in Help > About or in Programs and FeaturesAffected if The product is Adobe Acrobat DC, Adobe Acrobat Reader DC, Adobe Acrobat, or Adobe Acrobat Reader and version is in affected range
The environment is affected if Adobe Acrobat or Adobe Acrobat Reader is installed with a version falling within the specified vulnerable ranges and AcroForms processing is available, which is enabled by default.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpdate Adobe Acrobat Reader DC to a patched version beyond 2021.005.20060, 2020.004.30006, or 2017.011.30199. Avoid opening untrusted PDF files or visiting malicious web pages that deliver malicious AcroForm content.
Acrobat Reader DC/Acrobat DC version 2021.006.x or later, 2020.005.x or later, and 2017.012.x or later (or the latest available release)
- 1. Close all instances of Adobe Acrobat or Acrobat Reader
- 2. Navigate to the official Adobe download page: https://get.adobe.com/reader/ (for Reader) or https://get.adobe.com/acrobat/ (for Acrobat)
- 3. Download the latest version of the software
- 4. Run the installer and follow the prompts to complete the installation
- 5. Restart the application if it was open during installation
- 6. Verify the installed version by going to Help > About Adobe Acrobat/Reader
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation2.0 h
- Testing1.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-39840 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-39840 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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