Security readout for executives and security teams
Plain-English summary
This is a high-impact flaw in Foxit Reader 10.1.3.37598. A malicious PDF, or a malicious website when the browser plugin is enabled, can trigger memory corruption and potentially run attacker-controlled code. The user must open the file or visit the site.
Executive priority
Treat this as a priority endpoint remediation item, not an internet-facing emergency. The impact is severe if triggered, but available evidence requires user interaction and does not show confirmed active exploitation.
Technical view
CVE-2021-21831 is a CWE-416 use-after-free in Foxit Reader’s JavaScript engine. Talos reports that a specially crafted PDF can reuse freed memory and lead to arbitrary code execution. CVSS 3.0 is 8.8 with network attack vector and required user interaction.
Likely exposure
Exposure is likely limited to endpoints running Foxit Reader 10.1.3.37598, especially users who open PDFs from email, web downloads, or untrusted sources. Risk is higher where the Foxit browser plugin extension is enabled.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation evidence. Exploitation requires user interaction: opening a crafted PDF or visiting a crafted malicious site with the browser plugin enabled.
Researcher notes
Focus validation on exact version exposure, JavaScript-enabled PDF handling, and browser plugin presence. The provided sources establish RCE potential but do not provide confirmed exploitation in the wild or a named fixed version in the bundle.
Mitigation direction
- Check Foxit guidance for CVE-2021-21831 and update affected Reader installations accordingly.
- Prioritize removing or replacing Foxit Reader 10.1.3.37598 on managed endpoints.
- Disable the Foxit browser plugin extension where business use does not require it.
- Restrict untrusted PDF handling through email, web filtering, and attachment controls.
- Warn high-risk users not to open unexpected PDFs from external sources.
Validation and detection
- Inventory endpoints for Foxit Reader version 10.1.3.37598.
- Confirm whether the Foxit browser plugin extension is enabled in managed browsers.
- Review EDR and email telemetry for suspicious PDF handling activity.
- Verify patched or replaced installations through endpoint management reporting.
- Check vendor and Talos references for any updated remediation guidance.
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-2021-21831 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-2021-1294CVE 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.