Security readout for executives and security teams
Plain-English summary
CVE-2021-28631 is a high-severity Adobe Acrobat Reader DC flaw. A malicious file could run code as the person who opens it. The business risk is endpoint compromise through document handling, especially where users receive PDFs from external parties.
Executive priority
Treat this as a high-priority endpoint patching issue, not an internet-facing emergency. The main urgency is reducing document-borne compromise risk across staff workstations.
Technical view
The issue is a CWE-416 use-after-free in Acrobat Reader DC AcroForm Field handling. Affected versions include 2021.001.20155 and earlier, 2020.001.30025 and earlier, and 2017.011.30196 and earlier. CVSS 3.1 is 7.8: local attack vector, low complexity, no privileges, user interaction required, and high CIA impact.
Likely exposure
Exposure is most likely on user workstations running affected Adobe Acrobat Reader DC versions and opening externally supplied PDF files. Servers are only in scope if they use affected Reader software interactively or in document workflows.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation evidence. Exploitation requires user interaction: a victim must open a malicious file. Successful exploitation can execute arbitrary code in the current user's context.
Researcher notes
The available evidence identifies the bug class, product line, affected version thresholds, CVSS vector, and user-interaction requirement. The bundle does not provide exploit details, indicators, or fixed version numbers beyond the Adobe advisory reference.
Mitigation direction
- Inventory Acrobat Reader DC installations and identify affected versions listed in the CVE record.
- Check Adobe APSB21-37 for the applicable vendor security update or guidance.
- Prioritize updates for users who handle external PDFs or email attachments.
- Limit opening untrusted PDFs until affected Reader DC installations are updated.
Validation and detection
- Confirm installed Acrobat Reader DC versions against the affected version thresholds.
- Verify Adobe APSB21-37 guidance has been applied on managed endpoints.
- Review endpoint telemetry for suspicious activity after PDF opening events.
- Confirm PDF-handling workflows do not use affected Reader versions.
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-2021-28631 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 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/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:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H1.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.8HighVector: CVSS:3.1/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/apsb21-37.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.