Security readout for executives and security teams
Plain-English summary
This flaw can make Adobe Acrobat Reader DC crash when a user opens a malicious file. It does not indicate data theft or code execution in the supplied sources, but it can disrupt work on affected endpoints.
Executive priority
Treat this as a moderate endpoint availability issue. It is less urgent than code execution or data exposure, but still worth closing through normal patch management because exploitation needs only user interaction.
Technical view
CVE-2021-39849 is a CWE-476 null pointer dereference in Acrobat Reader DC. The CVSS 3.1 score is 5.5: local attack vector, low complexity, no privileges, required user interaction, and high availability impact only.
Likely exposure
Exposure is mainly desktops or virtual desktops running Acrobat Reader DC 2021.005.20060 and earlier, 2020.004.30006 and earlier, or 2017.011.30199 and earlier.
Exploitation context
The supplied sources say exploitation requires a victim to open a malicious file. CISA KEV status is false in the bundle, and no cited source confirms active exploitation.
Researcher notes
Evidence supports denial of service only: confidentiality and integrity impacts are none in the CVSS vector. The source bundle does not provide exploit details, fixed build numbers, or independent exploitation reporting beyond the Adobe reference.
Mitigation direction
- Review Adobe APSB21-55 for vendor-specified fixed versions and update guidance.
- Prioritize updating affected Acrobat Reader DC installations on managed endpoints.
- Warn users against opening unexpected PDF files from untrusted sources.
- Use email and web controls to reduce delivery of suspicious attachments.
Validation and detection
- Inventory Acrobat Reader DC versions across endpoints and VDI images.
- Flag installations at or below the affected version thresholds.
- Confirm whether Adobe APSB21-55 updates are installed where applicable.
- Review crash telemetry for Acrobat Reader instability after suspicious file opens.
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-2021-39849 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 (3.1)
- 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.