# CVE-2026-91817: Foxit PDF Editor heap-based out-of-bounds read in JavaScript string handling

Source: https://junglewise.ai/threats/cve-2026-91817-a-heap-based-out-of-bounds-read-vulnerability-exists-in-foxit-pdf  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-23. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-91817 · Severity: medium · CVSS 6.1 · Published 2026-09-23

Foxit PDF Editor and Reader are widely used applications that display and edit PDF documents. A flaw in how they process embedded JavaScript code that manipulates text strings can cause the application to crash or leak sensitive information from memory. An attacker could exploit this by sending a specially crafted PDF file that triggers the vulnerability when opened.

Technologies: [Foxit PDF Editor](https://junglewise.ai/threats/technologies/pdf-editor), [Foxit PDF Reader](https://junglewise.ai/threats/technologies/pdf-reader). Vendors: [Foxit](https://junglewise.ai/threats/vendors/foxit).

## Quick answers

**Is CVE-2026-91817 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-91817 being exploited in the wild.

**How severe is CVE-2026-91817?** Medium severity, with a CVSS score of 6.1, published 23 September 2026.

**Which products and versions are affected?** Foxit PDF Editor 2026.2.0.39747 and all previous 2026.x versions, 2025.3.0.35737 and all previous 2025.x versions, 2024.4.1.27687 and all previous 2024.x versions, 2023.3.0.23028 and all previous 2023.x versions, 14.0.7.33751 and all previous 14.x versions, 13.2.6.24111 and earlier; Foxit PDF Reader 2026.2.0.39747 and earlier.

**Is there a fix for CVE-2026-91817?** A patch was published on 2026-09-23: Foxit PDF Reader 2026.2.1 and Foxit PDF Editor 2026.2.1/14.0.8 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-91817 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-91817?** Check whether you run Foxit PDF Editor or Foxit PDF Reader at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A heap-based out-of-bounds read vulnerability exists in Foxit PDF Editor/Reader's PDF JavaScript engine when handling wide string deletion operations. Insufficient validation of string-deletion ranges leads to integer underflow, permitting out-of-bounds memory access. The vulnerability requires user interaction (opening a malicious PDF) and affects multiple versions across different product lines.

## Affected products

- Foxit PDF Reader 2026.2.0.39747 and earlier
- Foxit PDF Editor 2026.2.0.39747 and all previous 2026.x versions, 2025.3.0.35737 and all previous 2025.x versions, 2024.4.1.27687 and all previous 2024.x versions, 2023.3.0.23028 and all previous 2023.x versions, 14.0.7.33751 and all previous 14.x versions, 13.2.6.24111 and earlier

## Timeline

- 2026-09-23: disclosed
- 2026-09-23: patched: Foxit PDF Reader 2026.2.1 and Foxit PDF Editor 2026.2.1/14.0.8

## References

- [https://www.foxit.com/support/security-bulletins.html](https://www.foxit.com/support/security-bulletins.html)

## Related threats

- [Foxit PDF Editor use-after-free in JavaScript annotation handling](https://junglewise.ai/threats/cve-2026-91818-a-use-after-free-vulnerability-exists-in-foxit-pdf-editor-reader)
- [Foxit PDF Editor use-after-free in annotation handling](https://junglewise.ai/threats/cve-2026-91816-a-use-after-free-vulnerability-exists-in-foxit-pdf-editor-reader)
- [Foxit PDF Editor/Reader out-of-bounds write in JPEG2000 decoding](https://junglewise.ai/threats/cve-2026-91815-foxit-pdf-editor-reader-does-not-perform-sufficient-verification)
- [Foxit PDF Editor and Reader signature validation bypass in incremental updates](https://junglewise.ai/threats/cve-2026-91814-a-signature-validation-vulnerability-exists-in-foxit-pdf-editor)
- [Foxit PDF Reader/Editor update mechanism privilege escalation](https://junglewise.ai/threats/cve-2026-91813-a-vulnerability-in-foxit-pdf-editor-reader-s-update-mechanism)