Security readout for executives and security teams
Plain-English summary
CVE-2021-21044 is a high-severity Adobe Acrobat Reader DC flaw. A malicious JPEG opened by a user could let an attacker run code as that user. This is most urgent where staff routinely receive and open external documents or image attachments.
Executive priority
Prioritize remediation for user workstations that process external files. The flaw is not remotely exploitable without user action, but a common phishing or attachment workflow could still turn it into code execution on an employee device.
Technical view
The CVE describes a CWE-787 out-of-bounds write in Acrobat Reader DC JPEG parsing. Affected versions include 2020.013.20074 and earlier, 2020.001.30018 and earlier, and 2017.011.30188 and earlier. CVSS 3.0 is 7.8 with local attack vector and required user interaction.
Likely exposure
Exposure is likely on workstations running affected Acrobat Reader DC branches, especially where email, web downloads, or document workflows allow users to open untrusted files.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation evidence. Exploitation requires user interaction: the victim must open a malicious file. Successful exploitation could compromise confidentiality, integrity, and availability within the current user's context.
Researcher notes
Evidence is limited to the CVE record and Adobe advisory reference in the provided bundle. The bundle identifies the vulnerable component and version thresholds but does not provide exploit details, fixed build numbers, or observed exploitation claims.
Mitigation direction
- Inventory Acrobat Reader DC versions across endpoints.
- Use Adobe APSB21-09 to identify the appropriate security update.
- Upgrade affected installations according to Adobe guidance.
- Reduce handling of untrusted image or document attachments until remediated.
- Keep endpoint detection and attachment scanning enabled.
Validation and detection
- Confirm installed Reader versions are newer than listed affected versions.
- Check software deployment records for the Adobe update tied to APSB21-09.
- Review endpoint inventory for remaining 2017 or 2020 Reader branches.
- Verify high-risk users cannot bypass document security controls.
- Monitor for suspicious Reader crashes or child-process behavior.
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-2021-21044 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.