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AcrobatApplication · Adobe

CVE-2021-39851

MEDIUM · 5.5 CVSS v3.1 Published 2021-09-29
Fix available
A fix is available. Upgrade to after 21.005.20060 or later.
See remediation →
58/100
Remediation priority · Elevated
No privileges

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 · unedited
Acrobat Reader DC versions 2021.005.20060 (and earlier), 2020.004.30006 (and earlier) and 2017.011.30199 (and earlier) are affected by a Null pointer dereference vulnerability. An unauthenticated attacker could leverage this vulnerability to achieve an application denial-of-service 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 confidence

A null pointer dereference vulnerability in Adobe Acrobat Reader DC allows an unauthenticated attacker to cause a denial-of-service condition via a maliciously crafted PDF file. The victim must open the file for exploitation, which crashes the application in the context of the current user's session.

MitigationUpdate Adobe Acrobat Reader DC to the latest patched versions (2021.006.20060 or later for the 2021 track, 2021.001.20135 or later for 2020, 2021.001.20135 or later for 2017). Users should avoid opening untrusted PDF files.

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
AcrobatApplication
Affected:>= 20.001.30005, <= 20.004.30006>= 17.011.30059, <= 17.011.30199
Acrobat ReaderApplication
Affected:>= 20.001.30005, <= 20.004.30006>= 17.011.30059, <= 17.011.30199
Acrobat DcApplication
Affected:>= 15.008.20082, <= 21.005.20058>= 15.008.20082, <= 21.005.20060
Acrobat Reader DcApplication
Affected:>= 15.008.20082, <= 21.005.20058>= 15.008.20082, <= 21.005.20060

CVSS 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
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify the installed Adobe product name
    Open the application and go to Help > About Adobe Acrobat Reader (or Acrobat), or right-click the executable and select Properties to view the product name
    Affected if The product is Adobe Acrobat, Adobe Acrobat Reader, Adobe Acrobat DC, or Adobe Acrobat Reader DC
  2. Determine the exact version number of the installed Adobe application
    In the application, go to Help > About Adobe Acrobat Reader. The version is displayed in the format such as 21.005.20060 or 20.004.30006. Alternatively, on Windows check the version in the registry key HKLM\SOFTWARE\Adobe\Acrobat Reader\<version>\InstallPath
    Affected if The exact version cannot be determined or does not match the product version format mentioned
  3. Compare your version against the affected ranges
    Match your installed version against these vulnerable ranges: Acrobat/Reader 2020: 20.001.30005 to 20.004.30006; Acrobat/Reader 2017: 17.011.30059 to 17.011.30199; Acrobat DC/Reader DC: 15.008.20082 to 21.005.20058 (Classic) or 15.008.20082 to 21.005.20060 (Continuous)
    Affected if Your installed version falls within any of these ranges, meaning it is between the minimum and maximum vulnerable versions listed
  4. Verify if the application can open PDF files
    Attempt to open any PDF file in Adobe Acrobat Reader or Adobe Acrobat to confirm the application is functional
    Affected if The application crashes immediately upon opening a PDF file, which may indicate exploitation of this vulnerability

You are affected if you have Adobe Acrobat, Acrobat Reader, Acrobat DC, or Reader DC installed with a version number within the vulnerable ranges (20.001.30005-20.004.30006, 17.011.30059-17.011.30199, or 15.008.20082-21.005.20058/21.005.20060 depending on the product track).

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to a release after 21.005.20060
Interim mitigation

Update Adobe Acrobat Reader DC to the latest patched versions (2021.006.20060 or later for the 2021 track, 2021.001.20135 or later for 2020, 2021.001.20135 or later for 2017). Users should avoid opening untrusted PDF files.

Recommended fix High confidence

Upgrade to Adobe Acrobat/Reader DC 2021.006.20056 or later for the 2021 track; 2020.004.30007 or later for the 2020 track; 2017.011.30200 or later for the 2017 track

  1. 1. Verify the current installed version of Adobe Acrobat or Acrobat Reader by opening the application and navigating to Help > About Adobe Acrobat (or Reader).
  2. 2. Identify which product line and version branch applies to your installation (Acrobat/Reader Classic 2017, 2020, or Continuous).
  3. 3. Download the latest version of Adobe Acrobat or Acrobat Reader from the official Adobe website at https://get.adobe.com/reader/ (for Reader) or https://get.adobe.com/acrobat/ (for Acrobat).
  4. 4. Close all Adobe applications and any web browsers with PDF viewing capabilities.
  5. 5. Run the downloaded installer and follow the on-screen prompts to update the software.
  6. 6. After installation completes, restart the computer to ensure all components are properly updated.
  7. 7. Verify the new version by checking Help > About to confirm the installation was successful.
Caveat Upgrading may overwrite existing installations; ensure backup of personal settings if needed; some enterprise deployments may require IT-administered deployment

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Acrobat Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-39851 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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