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AcrobatApplication · Adobe

CVE-2021-39843

HIGH · 7.8 CVSS v3.1 Published 2021-09-29
Fix available
A fix is available. Upgrade to after 21.005.20060 or later.
See remediation →
81/100
Remediation priority · High
High EPSS 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 an out-of-bounds write vulnerability 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 confidence

Adobe Acrobat Reader DC contains an out-of-bounds write vulnerability in the listed affected versions. An attacker can craft a malicious PDF file that, when opened by a victim, triggers the out-of-bounds write, allowing arbitrary code execution in the context of the current user. Successful exploitation requires user interaction (opening the malicious file).

MitigationUpdate Adobe Acrobat Reader DC to a patched version beyond 2021.005.20060, 2020.004.30006, and 2017.011.30199. Alternatively, deploy compensating controls such as restricting PDF file handling or implementing email/web gateway filtering to block malicious PDF attachments.

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
High
Integrity
High
Availability
High

CVSS:3.1/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 checks

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

  1. Identify the installed Adobe Acrobat or Reader product
    On Windows, open the application and go to Help > About Adobe Acrobat (or Reader). On macOS, right-click the application in Applications and select Get Info. Note whether the product name includes 'DC' or is a classic (non-DC) version.
    Affected if The product is Adobe Acrobat or Adobe Acrobat Reader (any variant)
  2. Determine the exact version number
    Record the full version number shown in the About dialog (e.g., 20.004.30006, 17.011.30199, 21.005.20058). On Windows, you can also query the registry under HKLM\SOFTWARE\Adobe\Adobe Acrobat\[version] or HKLM\SOFTWARE\WOW6432Node\Adobe\Adobe Acrobat for the version value.
    Affected if A version number is retrieved from the installation
  3. Check if the version falls within the affected classic (non-DC) ranges
    Compare your version to these ranges: 20.001.30005 through 20.004.30006, or 17.011.30059 through 17.011.30199. If your version starts with 20.x, it must be >= 20.001.30005 and <= 20.004.30006. If it starts with 17.x, it must be >= 17.011.30059 and <= 17.011.30199.
    Affected if The version is between 20.001.30005 and 20.004.30006, or between 17.011.30059 and 17.011.30199
  4. Check if the version falls within the affected DC ranges
    If you have a DC variant, compare your version to: 15.008.20082 through 21.005.20058, or 15.008.20082 through 21.005.20060. Note that DC versions have broader ranges covering multiple years of releases.
    Affected if The DC version is between 15.008.20082 and 21.005.20058, or between 15.008.20082 and 21.005.20060

You are affected if the installed Adobe Acrobat or Reader version matches one of the listed affected version ranges for either the classic or DC product line.

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 a patched version beyond 2021.005.20060, 2020.004.30006, and 2017.011.30199. Alternatively, deploy compensating controls such as restricting PDF file handling or implementing email/web gateway filtering to block malicious PDF attachments.

Recommended fix High confidence

Adobe Acrobat/Reader 2021.005.20061+ (Classic 2021), 2020.004.30007+ (Classic 2020), 2017.011.30200+ (Classic 2017), or 21.005.20060.20093+ / 20.004.30006.20093+ (Continuous track)

  1. 1. Identify the currently installed Adobe Acrobat or Acrobat Reader version by opening the application, selecting 'Help' > 'About Adobe Acrobat/Reader'
  2. 2. Based on your current version, determine the appropriate upgrade path: Classic 2021 track: upgrade to version 2021.005.20061 or later; Classic 2020 track: upgrade to version 2020.004.30007 or later; Classic 2017 track: upgrade to version 2017.011.30200 or later; Continuous track: upgrade to version 21.005.20060.20093 or later for 2021, or 20.004.30006.20093 or later for 2020
  3. 3. Download the fixed version from the official Adobe Acrobat download page at https://get.adobe.com/reader/ (for Reader) or https://get.adobe.com/acrobat/ (for Acrobat), or obtain via your organization's software distribution system
  4. 4. Close all instances of Adobe Acrobat/Reader
  5. 5. Run the installer and follow the prompts to complete the upgrade
  6. 6. Verify the upgrade was successful by checking Help > About to confirm the version matches or exceeds the fixed version for your track
Caveat Standard minor version upgrade with no expected breaking changes; ensure compatibility with your PDF workflows and any integrated plugins

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

Fix this in Acrobat Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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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-2021-39843 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