dbcve.org
AcrobatApplication · Adobe

CVE-2021-39856

MEDIUM · 6.5 CVSS v3.1 Published 2021-09-29
Fix available
A fix is available. Upgrade to after 21.005.20060 or later.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable 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 ActiveX Control versions 2021.005.20060 (and earlier), 2020.004.30006 (and earlier) and 2017.011.30199 (and earlier) are affected by an Information Disclosure vulnerability. An unauthenticated attacker could leverage this vulnerability to obtain NTLMv2 credentials. Exploitation of this issue requires user interaction in that a victim must visit an attacker controlled web page.

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 ActiveX control contains an information disclosure vulnerability allowing unauthenticated attackers to capture NTLMv2 credentials via malicious web pages. The vulnerability is triggered when a victim visits an attacker-controlled website, which causes the ActiveX control to inadvertently transmit NTLMv2 authentication credentials.

MitigationUpdate Adobe Acrobat Reader DC to a version newer than 2021.005.20060 (Continuous track), 2020.004.30006 (Classic 2020), or 2017.011.30199 (Classic 2017). Additionally, organizations should consider enabling SMB signing and disabling NTLM authentication where possible to mitigate credential theft risks.

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:>= 17.011.30059, <= 17.011.30199>= 20.001.30005, <= 20.004.30006
Acrobat ReaderApplication
Affected:>= 17.011.30059, <= 17.011.30199>= 20.001.30005, <= 20.004.30006
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
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

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. Confirm Adobe Acrobat or Reader installation
    Open Windows Control Panel, go to Programs and Features, and look for Adobe Acrobat or Adobe Acrobat Reader in the installed programs list
    Affected if Either Adobe Acrobat or Adobe Acrobat Reader is installed on the system
  2. Identify installed version number
    Right-click the Adobe application in Programs and Features, select Properties, and note the version shown in the Version field
    Affected if The version displayed falls within any of these ranges: 17.011.30059 to 17.011.30199, 20.001.30005 to 20.004.30006, 15.008.20082 to 21.005.20058, or 15.008.20082 to 21.005.20060
  3. Check for ActiveX control presence
    Open Windows Registry Editor and navigate to HKLM\SOFTWARE\Microsoft\Code Store Database\Distribution Units or HKCU\SOFTWARE\Microsoft\Code Store Database\Distribution Units, look for keys related to Acrobat or Adobe PDF
    Affected if An ActiveX control entry for Adobe Acrobat or Adobe Acrobat Reader exists in the Windows registry
  4. Verify Windows integration
    Open Internet Explorer or Edge and type about:addons, look for Adobe Acrobat or Adobe PDF Reader add-on enabled in the browser
    Affected if The Adobe ActiveX control add-on is enabled in any web browser on the system

System is affected if Adobe Acrobat or Reader is installed with a version matching the affected ranges and the ActiveX control component is present and enabled on the system.

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 version newer than 2021.005.20060 (Continuous track), 2020.004.30006 (Classic 2020), or 2017.011.30199 (Classic 2017). Additionally, organizations should consider enabling SMB signing and disabling NTLM authentication where possible to mitigate credential theft risks.

Recommended fix High confidence

Upgrade to versions beyond the affected range: 2021.006.x or later for 2021.x releases, 2020.005.x or later for 2020.x releases, 2017.012.x or later for 2017.x releases, or the latest available version

  1. 1. Open Adobe Acrobat or Acrobat Reader on your system
  2. 2. Navigate to Help > Check for Updates (or use the Help menu)
  3. 3. Allow Adobe to check for available updates
  4. 4. If updates are available, review the update details to confirm it includes the fix for CVE-2021-39856
  5. 5. Download and install all available updates
  6. 6. Restart the application after installation
  7. 7. Alternatively, download the latest version directly from https://get.adobe.com/reader/ (for Reader) or https://get.adobe.com/acrobat/ (for Acrobat)
  8. 8. Verify the installed version by going to Help > About Adobe Acrobat [Reader] DC
Caveat Standard upgrade risk: ensure compatibility with existing PDF workflows and plugins before deploying organization-wide

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
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,424.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-39856 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2021-39856 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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