CVE-2021-39838
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 in the processing of the AcroForm buttonGetCaption action that could result in arbitrary code execution in the context of the current user. Exploitation of this issue requires user interaction in that a victim must 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 confidenceUse-after-free vulnerability in Adobe Acrobat Reader DC's processing of AcroForm buttonGetCaption actions. When processing specially crafted PDF files with malicious AcroForm button elements, the software fails to properly manage memory, leading to memory corruption that can be exploited for arbitrary code execution in the context of the current user.
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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Identify the installed Adobe productOpen Adobe Acrobat Reader or Adobe Acrobat, then navigate to Help > About Adobe Acrobat Reader (or About Adobe Acrobat) to see the exact product name and version number.Affected if The product is Adobe Acrobat Reader DC, Adobe Acrobat DC, Adobe Acrobat, or Adobe Acrobat Reader and the version falls within the affected ranges.
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Compare installed version to affected rangesNote the full version number from the About dialog. For Adobe Acrobat Reader DC/Acrobat DC, check if version is >= 15.008.20082 and <= 21.005.20058 or <= 21.005.20060. For Adobe Acrobat/Reader (non-DC), check if version is >= 20.001.30005 and <= 20.004.30006, or >= 17.011.30059 and <= 17.011.30199.Affected if The installed version matches any of the listed affected version ranges.
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Verify AcroForm functionality is accessibleOpen any PDF file in the application and look for the Forms menu or toolbar. In Reader, go to View > Tools > Forms to see if form tools are available. AcroForm is a built-in feature enabled by default.Affected if The Forms tools are present and the application can process PDF forms containing AcroForm button elements.
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Check for recent PDF processing activityReview recently opened PDF files or check the application's recent documents list for PDF files that may contain interactive form elements, particularly those from untrusted sources.Affected if The user has recently opened PDF files, especially from untrusted sources, that could contain malicious AcroForm button elements.
A user is affected if Adobe Acrobat Reader DC, Adobe Acrobat DC, Adobe Acrobat, or Adobe Acrobat Reader is installed with a version number matching any of the affected ranges and the application processes PDF files with AcroForm content.
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 the latest patched version. As a defense-in-depth measure, disable JavaScript execution in Acrobat Reader settings and exercise caution when opening PDF files from untrusted sources.
Adobe Acrobat Reader DC 2021.006.20060 or later / Adobe Acrobat DC 2021.006.20060 or later (for the 2021 track); Acrobat 2020.004.30007 or later (for the 2020 track); Acrobat 2017.011.30200 or later (for the 2017 track)
- 1. Determine your current Adobe Acrobat or Acrobat Reader version by opening the application and navigating to Help > About Adobe Acrobat (or About Adobe Acrobat Reader)
- 2. Close all Adobe Acrobat/Reader applications
- 3. Download the latest version of Adobe Acrobat or Acrobat Reader DC from the official Adobe website (get.adobe.com/reader for Reader, or adobe.com/acrobat for Acrobat)
- 4. Run the installer and follow the prompts to complete the upgrade
- 5. After installation, verify the new version by checking Help > About to confirm you are running a version newer than the affected releases
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-2021-39838 — 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-2021-39838 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
- No spam, self-promotion, credentials, or personal data