Security readout for executives and security teams
Plain-English summary
A malicious PDF opened in vulnerable Adobe Acrobat Reader DC could let an attacker run code as the current user. This is serious for phishing-driven compromise, but the provided sources require user interaction and do not show known active exploitation.
Executive priority
Treat as a high-priority endpoint patching issue, especially in environments with frequent PDF exchange. The business risk is phishing-assisted code execution on user workstations, not unauthenticated network compromise.
Technical view
CVE-2021-21058 is a CWE-787 memory corruption issue in Acrobat Reader DC PDF parsing. A specially crafted PDF can trigger arbitrary code execution with current-user privileges. CVSS 3.0 is 7.8: local attack vector, low complexity, no privileges required, user interaction required, and high confidentiality, integrity, and availability impact.
Likely exposure
Organizations are exposed where Adobe Acrobat Reader DC versions 2020.013.20074 and earlier, 2020.001.30018 and earlier, or 2017.011.30188 and earlier are installed and users can open untrusted PDFs.
Exploitation context
The source bundle says exploitation requires a victim to open a malicious file. KEV is false, and no provided source states active exploitation, public exploit availability, or exploitation in the wild.
Researcher notes
Evidence supports arbitrary code execution through crafted PDF parsing in current-user context. The bundle does not provide exploit details, fixed version numbers, or proof of exploitation. Validate exposure by product version and user PDF handling paths.
Mitigation direction
- Review Adobe APSB21-09 for vendor-directed updates and affected product details.
- Update Acrobat Reader DC installations covered by the listed vulnerable version branches.
- Limit opening of untrusted PDF attachments until affected systems are updated.
- Use email and web controls to reduce delivery of suspicious PDF files.
Validation and detection
- Inventory Acrobat Reader DC versions across managed endpoints.
- Confirm vulnerable branches are no longer at or below the listed affected versions.
- Verify update deployment status against Adobe APSB21-09 guidance.
- Review mail and endpoint alerts for suspicious PDF delivery or opening.
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-2021-21058 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.