Security readout for executives and security teams
Plain-English summary
This flaw lets a malicious document trigger operating-system command execution through Adobe Acrobat Reader. A victim must open the malicious file, but successful exploitation can run code as that user and affect confidentiality, integrity, and availability.
Executive priority
Treat as high priority for endpoint patching, especially where staff handle external PDFs or documents. It is not described as remotely exploitable without user action, but the potential impact is full code execution as the user.
Technical view
CVE-2021-28634 is CWE-78 command injection in Acrobat Reader's AcrobatUtils.scpt extension. Affected Reader DC versions include 2021.005.20054 and earlier, 2020.004.30005 and earlier, and 2017.011.30197 and earlier. CVSS 3.1 is 8.2 with local attack vector, low complexity, required privileges, user interaction, and changed scope.
Likely exposure
Exposure is most likely on user workstations running the listed Acrobat Reader DC versions where users can receive and open attacker-supplied files. The source bundle does not establish server-side exposure or broader Adobe product impact.
Exploitation context
The provided sources do not show CISA KEV listing or confirmed active exploitation. Exploitation requires user interaction: a victim opens a malicious file. Impact is arbitrary code execution in the current user's context.
Researcher notes
The key uncertainty is platform and fixed-version detail beyond the affected Reader DC builds named in the CVE description. Avoid assuming active exploitation. Validate exposure by version inventory and use Adobe's bulletin for authoritative remediation details.
Mitigation direction
- Review Adobe APSB21-51 and apply the vendor-recommended Acrobat Reader updates.
- Inventory endpoints for Acrobat Reader DC versions at or below the listed affected builds.
- Reduce exposure to untrusted documents until affected installations are remediated.
- Prioritize systems used for email, web downloads, and external document handling.
Validation and detection
- Confirm installed Acrobat Reader versions across managed endpoints.
- Flag Reader DC 2021.005.20054, 2020.004.30005, 2017.011.30197, and earlier builds.
- Verify Adobe APSB21-51 remediation status through software inventory or patch management records.
- Review endpoint alerts involving Acrobat Reader launching unusual child processes.
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-78: Command execution behavior lookup
Command injection weaknesses can lead defenders to review execution techniques and command interpreter telemetry. 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-2021-28634 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
- 8.2 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/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:L/UI:R/S:C/C:H/I:H/A:H1.56Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.2HighVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://helpx.adobe.com/security/products/acrobat/apsb21-51.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.
Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.