Security readout for executives and security teams
Plain-English summary
This vulnerability can crash Adobe Acrobat Reader DC when a user opens a malicious file. It does not indicate data theft or system takeover in the provided sources, but it can disrupt document workflows for affected users.
Executive priority
Treat this as a moderate endpoint hygiene issue. It is not described as remote code execution, but outdated Reader installations can create avoidable disruption and should be patched through normal endpoint management.
Technical view
CVE-2021-39850 is a CWE-476 null pointer dereference in Acrobat Reader DC. Affected versions include 2021.005.20060 and earlier, 2020.004.30006 and earlier, and 2017.011.30199 and earlier. The CVSS 3.1 score is 5.5, with availability impact only.
Likely exposure
Exposure is likely where legacy Adobe Acrobat Reader DC builds remain installed, especially on endpoints that routinely open PDFs from email, web downloads, or external parties.
Exploitation context
The sources state exploitation requires user interaction: the victim must open a malicious file. CISA KEV status is false in the provided bundle, so active exploitation is not established here.
Researcher notes
The vulnerability is availability-only under CVSS, with AV:L and UI:R. The provided evidence does not include exploit code, proof of exploitation, or detailed root cause beyond null pointer dereference.
Mitigation direction
- Update affected Acrobat Reader DC installations using Adobe APSB21-55 guidance.
- Prioritize endpoints running versions at or below the affected builds.
- Restrict or warn on untrusted PDF attachments where practical.
- Check Adobe guidance for any product-specific remediation details.
Validation and detection
- Inventory Acrobat Reader DC versions across managed endpoints.
- Flag versions 2021.005.20060, 2020.004.30006, 2017.011.30199, or earlier.
- Confirm patched systems no longer report affected Reader builds.
- Review endpoint crash telemetry for suspicious Reader crash clusters.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
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CWE-476: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-39850 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H1.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://helpx.adobe.com/security/products/acrobat/apsb21-55.htmlCVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
NULL Pointer Dereference
NULL Pointer Dereference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.