Security readout for executives and security teams
Plain-English summary
This vulnerability affects older Adobe Acrobat Reader versions when a user opens a malicious PDF. The issue can corrupt memory under the user’s account, mainly risking application crash or limited data tampering rather than direct data theft. Business urgency is moderate because exploitation needs user interaction and no provided source states active exploitation.
Executive priority
Treat as a moderate endpoint hygiene issue. The main business risk is user-driven PDF exposure on outdated Reader installations, not confirmed active exploitation. Remediate through routine patch management, with faster action for teams that regularly process external documents.
Technical view
CVE-2021-39846 is a CWE-121 stack overflow in Adobe Acrobat Reader’s handling of crafted PDF content, described as a recursive /Parent property issue. Affected Reader versions include 2021.005.20060 and earlier, 2020.004.30006 and earlier, and 2017.011.30199 and earlier. CVSS 3.1 is 6.1 with local attack vector and required user interaction.
Likely exposure
Exposure is most likely on endpoints where users still run the listed Acrobat Reader versions and open PDFs from email, web downloads, shared drives, or external parties. Systems using fully updated Reader versions are less likely to be exposed, but the provided sources do not list exact fixed versions.
Exploitation context
The source bundle does not report active exploitation, and KEV status is false. Exploitation requires a victim to open a crafted PDF in Acrobat Reader. The stated impact is memory corruption in the context of the current user, with high availability impact and low integrity impact.
Researcher notes
Evidence is limited to the CVE description, CVSS vector, affected version ranges, CWE-121, KEV=false, and Adobe APSB21-55 reference. The bundle does not provide exploit telemetry, proof-of-concept status, or exact fixed build numbers. Avoid validation using crafted PDFs in production.
Mitigation direction
- Update affected Acrobat Reader installations according to Adobe APSB21-55 guidance.
- Prioritize users who frequently handle external or unsolicited PDF files.
- Restrict opening PDFs from untrusted sources where practical.
- Use endpoint controls to reduce exposure to suspicious PDF attachments.
- Check Adobe guidance for exact fixed versions and deployment instructions.
Validation and detection
- Inventory Acrobat Reader versions across managed endpoints.
- Flag versions 2021.005.20060, 2020.004.30006, 2017.011.30199, and earlier.
- Confirm update deployment through software management or endpoint telemetry.
- Review email and web controls for external PDF handling.
- Verify no unsupported Reader tracks remain in production.
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-121: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-39846 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/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:L/A:H1.84.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.1MediumVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/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.
Stack-based Buffer Overflow
Stack-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.