Security readout for executives and security teams
Plain-English summary
This flaw affects older Adobe Acrobat Reader versions when a user opens a specially crafted PDF. It can corrupt memory under the current user account, mainly creating denial-of-service risk and limited integrity impact. It is not described as remotely exploitable without user interaction.
Executive priority
Treat this as a normal endpoint patching priority, not an emergency, unless your environment has broad exposure to untrusted PDFs or sensitive user workstations remain outdated.
Technical view
CVE-2021-39845 is a CWE-121 stack overflow in Acrobat Reader DC caused by insecure handling of a crafted PDF, described as a recursive page tree node issue. CVSS 3.1 is 6.1 with local attack vector, no privileges required, and required user interaction.
Likely exposure
Exposure is primarily on endpoints where users run Acrobat Reader DC 2021.005.20060 or earlier, 2020.004.30006 or earlier, or 2017.011.30199 or earlier.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation. Exploitation requires a victim to open a crafted PDF in Acrobat Reader, so email, downloads, and document-sharing workflows are the realistic delivery paths.
Researcher notes
The public record supports memory corruption from crafted PDF parsing, but does not provide exploit detail or confirmed exploitation. Validate exposure by version and deployment channel rather than by network scanning.
Mitigation direction
- Inventory Acrobat Reader versions across managed endpoints.
- Apply Adobe guidance from APSB21-55 and update affected Acrobat Reader installations.
- Restrict handling of unsolicited PDFs until Reader is updated.
- Use endpoint controls to reduce risky PDF launch paths.
Validation and detection
- Confirm installed Reader versions exceed the affected versions listed in the CVE record.
- Verify Adobe APSB21-55 remediation guidance was applied to managed endpoints.
- Review email and endpoint telemetry for suspicious PDFs targeting Reader users.
- Confirm users cannot run unsupported Reader release tracks.
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-2021-39845 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.