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 code execution in the supplied sources, but it can disrupt users who rely on Reader for business workflows.
Executive priority
Treat as a routine endpoint patching issue unless PDF crashes would disrupt critical operations. Business risk is service interruption, not confirmed compromise, based on supplied evidence.
Technical view
CVE-2021-39854 is a CWE-476 null pointer dereference in Acrobat Reader DC versions 2021.005.20060 and earlier, 2020.004.30006 and earlier, and 2017.011.30199 and earlier. CVSS 3.0 is 5.5, with local attack vector, required user interaction, no privileges, and availability impact only.
Likely exposure
Exposure is mainly endpoint-based where affected Acrobat Reader DC versions are installed and users open files from email, web downloads, portals, or external parties.
Exploitation context
The supplied data does not show active exploitation or KEV listing. Exploitation requires user interaction: a victim must open a malicious file. The stated outcome is application denial-of-service in the current user's context.
Researcher notes
The bundle provides affected version thresholds, CVSS vector, CWE-476, and user-interaction requirement. It does not provide CPEs, exploit evidence, or detailed fixed-version text, so remediation should be anchored to Adobe APSB21-55.
Mitigation direction
- Inventory Acrobat Reader DC versions across managed endpoints.
- Check Adobe APSB21-55 for vendor remediation guidance.
- Update affected Reader installations according to Adobe guidance.
- Warn users against opening unexpected or untrusted files.
- Prioritize users whose work depends heavily on PDF access.
Validation and detection
- Check for Reader versions at or below listed affected builds.
- Confirm updated builds match Adobe advisory guidance.
- Review endpoint crash telemetry for recurring Reader failures.
- Verify the CVE is not listed as KEV in supplied data.
- Document any systems that cannot be promptly updated.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-476: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-39854 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.5 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/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:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H1.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
5.5MediumVector: CVSS:3.0/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.