Security readout for executives and security teams
Plain-English summary
This flaw lets a malicious PDF trigger code execution when opened in affected Adobe Acrobat Reader DC versions. It requires user interaction, but the impact is serious because successful exploitation runs code as the current user, potentially exposing files, credentials, and endpoint access.
Executive priority
Treat this as a high-priority endpoint patching issue, not an internet-exposed infrastructure emergency. The main business risk is user-driven compromise through malicious PDFs on outdated Reader installations.
Technical view
CVE-2021-39836 is a CWE-416 use-after-free in Acrobat Reader DC AcroForm buttonGetIcon processing. Affected versions include 2021.005.20060 and earlier, 2020.004.30006 and earlier, and 2017.011.30199 and earlier. CVSS 3.0 is 7.8, with local attack vector, low complexity, no privileges, and required user interaction.
Likely exposure
Exposure is most likely on endpoints with older Adobe Acrobat Reader DC installed, especially users who receive PDFs from email, web downloads, document portals, or external parties. The bundle does not identify server-side exposure or non-Reader Adobe products.
Exploitation context
The source bundle states exploitation requires a victim to open a malicious file. It does not cite CISA KEV listing, active exploitation, public exploit availability, or observed campaigns, so active exploitation should not be assumed from these sources.
Researcher notes
The provided evidence is limited to CVE metadata and Adobe’s advisory reference. It supports high impact and user-interaction requirements, but does not establish exploit-in-the-wild status, exploit maturity, or exact fixed build numbers within the prompt bundle.
Mitigation direction
- Inventory Adobe Acrobat Reader DC installations and versions across endpoints.
- Review Adobe APSB21-55 for fixed Reader builds and deployment guidance.
- Prioritize systems where users routinely receive or open external PDF files.
- Limit handling of untrusted PDFs until updates are confirmed.
Validation and detection
- Compare installed Reader versions with Adobe APSB21-55 affected and fixed version guidance.
- Confirm whether any endpoints run 2021.005.20060, 2020.004.30006, 2017.011.30199, or earlier.
- Verify update deployment through endpoint management or software inventory records.
- Check security monitoring for suspicious PDF-open events where telemetry is available.
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-416: 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 lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-39836 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
- High
- CVSS
- 7.8 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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:H/I:H/A:H1.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
7.8HighVector: CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.