Security readout for executives and security teams
Plain-English summary
CVE-2021-40726 is a high-severity Adobe Acrobat Reader flaw that can let malicious PDF content run code as the signed-in user. Exploitation requires user interaction, such as opening a crafted file or visiting a malicious page. The bundle does not show public active exploitation or CISA KEV listing.
Executive priority
Prioritize normal high-severity endpoint patching, with urgency for users who handle external PDFs. This is not presented as actively exploited in the supplied evidence, but the impact is full code execution as the user.
Technical view
The issue is a CWE-416 use-after-free in Acrobat Reader DC AcroForm field processing. Affected versions include 2021.005.20060 and earlier, 2020.004.30006 and earlier, and 2017.011.30199 and earlier. Successful exploitation can cause arbitrary code execution with current-user privileges.
Likely exposure
Exposure is most likely on endpoints running affected Acrobat Reader DC release tracks, especially where users receive PDFs from email, web downloads, portals, or external partners. Servers are less likely to be directly exposed unless they process PDFs interactively with Reader.
Exploitation context
The source bundle states user interaction is required: the target must open a malicious file or visit a malicious page. KEV is false, and no provided source states active exploitation. Treat exploit status as unconfirmed from the supplied evidence.
Researcher notes
The CVSS vector is 7.8 with AV:L, AC:L, PR:N, UI:R, and high confidentiality, integrity, and availability impact. The key technical detail is AcroForm field use-after-free. The bundle does not provide exploit details, fixed build numbers, or telemetry evidence.
Mitigation direction
- Follow Adobe APSB21-55 guidance for Acrobat Reader updates.
- Prioritize endpoints on affected 2021, 2020, and 2017 Reader tracks.
- Reduce exposure to untrusted PDFs from email and web sources.
- Run Reader with least-privileged user accounts where possible.
- Check vendor guidance for any additional supported mitigations.
Validation and detection
- Inventory Acrobat Reader DC versions across managed endpoints.
- Confirm no systems run 2021.005.20060, 2020.004.30006, 2017.011.30199, or earlier.
- Review email and web controls for untrusted PDF delivery paths.
- Monitor Reader process activity for unexpected code execution indicators.
- Document patch status against Adobe APSB21-55.
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-2021-40726 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/apsb21-55.htmlCVE reference · x_refsource_MISC
- https://www.zerodayinitiative.com/advisories/ZDI-21-1249/CVE 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.