Security readout for executives and security teams
Plain-English summary
This vulnerability affects older Adobe Acrobat Reader DC releases. A malicious PDF or similar file could cause Acrobat to reveal sensitive memory from the local machine. It does not allow direct takeover by itself, but the memory disclosure could help defeat defenses such as ASLR during a broader attack.
Executive priority
Treat this as a moderate endpoint remediation item. It requires user action and is not listed as actively exploited, but it can expose sensitive memory and support more advanced attack chains.
Technical view
CVE-2021-39859 is a CWE-416 use-after-free issue in Acrobat Reader DC versions 2021.005.20060 and earlier, 2020.004.30006 and earlier, and 2017.011.30199 and earlier. CVSS 3.1 is 5.5 with user interaction required and high confidentiality impact only.
Likely exposure
Exposure is most likely on endpoints running the listed Acrobat Reader DC versions, especially where users open documents from email, web downloads, or external parties.
Exploitation context
The source bundle says exploitation requires user interaction: the victim must open a malicious file. KEV is false, and no cited source in the bundle states active exploitation.
Researcher notes
The record has a product naming mismatch: the title says Acrobat Pro DC, while the description names Acrobat Reader DC. Use the vendor advisory as the authoritative source for exact product and fixed-version mapping.
Mitigation direction
- Review Adobe APSB21-55 for vendor update guidance.
- Inventory and prioritize affected Acrobat Reader DC versions.
- Update affected installations according to Adobe guidance.
- Limit handling of untrusted documents until remediation is confirmed.
Validation and detection
- Check installed Acrobat Reader DC versions across managed endpoints.
- Compare versions against the affected thresholds in the CVE description.
- Confirm remediation status against Adobe APSB21-55.
- Verify users handling external files are included in rollout scope.
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 lookupCVE-2021-39859 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:H/I:N/A:N
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:H/I:N/A:N1.83.6Primary 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:H/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://helpx.adobe.com/security/products/acrobat/apsb21-55.htmlCVE reference · vendor-advisory
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.