Security readout for executives and security teams
Plain-English summary
This is a high-severity Adobe Acrobat Reader DC flaw that could let an attacker run code on a user's computer if the user opens a malicious file. The risk is mainly endpoint compromise through document handling, not unauthenticated server takeover.
Executive priority
Treat as a high-priority endpoint patching issue because successful exploitation can give an attacker code execution as the current user. Urgency is higher for teams handling outside documents, but the bundle does not show confirmed active exploitation.
Technical view
CVE-2021-21033 is a CWE-416 use-after-free vulnerability in Acrobat Reader DC versions 2020.013.20074 and earlier, 2020.001.30018 and earlier, and 2017.011.30188 and earlier. CVSS 3.0 is 8.8 with low attack complexity, no privileges required, and user interaction required.
Likely exposure
Organizations are exposed if users still run the affected Acrobat Reader DC versions, especially on workstations that receive external PDFs or other untrusted documents. Exposure depends on endpoint software inventory and patch status.
Exploitation context
The bundle states exploitation requires user interaction: a victim must open a malicious file. It does not identify public exploit use, and KEV status is false, so active exploitation should not be assumed from these sources.
Researcher notes
Evidence is limited to the CVE data and Adobe advisory reference. The vulnerability class is use-after-free, with network attack vector but required user interaction. Do not infer exploit availability, affected non-Reader products, or exact fixed versions beyond vendor guidance.
Mitigation direction
- Check Adobe APSB21-09 for vendor-fixed versions and deployment guidance.
- Update affected Acrobat Reader DC installations according to Adobe guidance.
- Prioritize endpoints that process external or unsolicited documents.
- Train users to treat unexpected PDF files as suspicious.
- Confirm software update tooling covers Acrobat Reader DC variants.
Validation and detection
- Inventory Acrobat Reader DC versions across managed endpoints.
- Flag installations at or below the affected version thresholds.
- Verify patch deployment against Adobe APSB21-09 guidance.
- Review endpoint detections for suspicious document-opening activity.
- Confirm high-risk user groups received the update first.
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-2021-21033 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
- 8.8 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/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:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H2.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
8.8HighVector: CVSS:3.0/AV:N/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.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.