Security readout for executives and security teams
Plain-English summary
CVE-2021-40420 is a high-severity flaw in Foxit Reader 11.1.0.52543. A malicious PDF, or a malicious website when the Foxit browser plugin is enabled, can lead to arbitrary code execution after user interaction.
Executive priority
Treat as a priority endpoint remediation item where the affected Foxit version is deployed. Business risk is highest for teams processing external PDFs, because exploitation depends on convincing a user to open content.
Technical view
The issue is a CWE-416 use-after-free in Foxit Reader's JavaScript engine. A crafted PDF can cause reuse of freed memory and potentially execute attacker-controlled code. CVSS 3.0 score is 8.8 with network attack vector and required user interaction.
Likely exposure
Exposure is most likely on user endpoints running Foxit Reader 11.1.0.52543, especially where Foxit opens PDFs by default or the browser plugin extension is enabled.
Exploitation context
The sources describe user-assisted exploitation through a crafted PDF or malicious site with the browser plugin enabled. The bundle does not show CISA KEV listing or other evidence of active exploitation.
Researcher notes
The provided evidence identifies Foxit Reader 11.1.0.52543 and the JavaScript engine use-after-free condition, but does not include detailed patch information. Avoid assuming broader Foxit product impact without vendor confirmation.
Mitigation direction
- Inventory endpoints for Foxit Reader 11.1.0.52543.
- Check Foxit or Talos guidance for confirmed fixes or mitigations.
- Disable the Foxit browser plugin extension where not required.
- Limit untrusted PDF handling on affected endpoints until remediated.
- Apply any vendor-confirmed update after validation.
Validation and detection
- Confirm installed Foxit Reader build numbers through software inventory.
- Review browser configurations for enabled Foxit plugin extensions.
- Identify users or systems that routinely handle external PDFs.
- Check EDR and email telemetry for suspicious PDF delivery patterns.
- Track remediation evidence against affected endpoint inventory.
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-2021-40420 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://talosintelligence.com/vulnerability_reports/TALOS-2021-1429CVE 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.