Security readout for executives and security teams
Plain-English summary
CVE-2021-21063 is a high-severity Adobe Acrobat Reader flaw. A malicious PDF can corrupt memory and may let an attacker run code as the logged-in user. The user must open the file, so phishing and document-sharing workflows are the main business concern.
Executive priority
Treat this as a prompt endpoint patching item, especially for teams that process outside PDFs. It is not presented here as actively exploited, but the impact is code execution and the attack path fits common phishing workflows.
Technical view
The issue is a CWE-787 memory corruption vulnerability in Acrobat Reader DC PDF parsing. A specially crafted PDF can trigger arbitrary code execution in the current user's context. The CVSS 3.0 score is 7.8, with local attack vector, low complexity, no privileges required, and required user interaction.
Likely exposure
Exposure is likely on endpoints running Acrobat Reader DC 2020.013.20074 or earlier, 2020.001.30018 or earlier, or 2017.011.30188 or earlier. Risk is highest for users who routinely open PDFs from email, web downloads, customer portals, or external file-sharing systems.
Exploitation context
The provided sources do not show CISA KEV listing or other cited evidence of active exploitation. Exploitation requires convincing a victim to open a malicious PDF. Successful exploitation could affect confidentiality, integrity, and availability within the current user's privileges.
Researcher notes
The source bundle identifies affected version thresholds but provides no CPEs. Use Adobe APSB21-09 and the CVE record as the authoritative scope references. Do not assert exploitation in the wild from this bundle; KEV is false and no cited source supports that claim.
Mitigation direction
- Review Adobe APSB21-09 and apply Adobe's security updates for Acrobat Reader.
- Inventory Acrobat Reader versions across managed endpoints.
- Prioritize users handling external PDFs, email attachments, or shared documents.
- Remove or isolate unsupported affected Reader versions where updates are unavailable.
- Reinforce handling controls for unsolicited or unexpected PDF files.
Validation and detection
- Confirm installed Reader versions are newer than the affected build thresholds.
- Verify endpoint management reports successful Adobe security update deployment.
- Check high-risk user groups for remaining affected versions.
- Review security telemetry for suspicious PDF-driven alerts, without assuming exploitation.
- Document remediation status against APSB21-09 guidance.
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-787: 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-2021-21063 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/apsb21-09.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.
Out-of-bounds Write
Out-of-bounds Write represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.