# CVE-2026-101039: FAST FAC1900R stack buffer overflow in devdiscover service

Source: https://junglewise.ai/threats/cve-2026-101039-a-vulnerability-was-identified-in-fast-fac1900r-20190827-2-0-2  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-28. Updated: 2026-09-28  
License: CC BY 4.0 with a link back

CVE-2026-101039 · Severity: critical · CVSS 10 · Published 2026-09-28

The FAST FAC1900R is a network router used for LAN connectivity and device discovery. A stack buffer overflow vulnerability in its devdiscover service can be triggered remotely via specially crafted UDP packets, allowing an attacker to crash the device or execute arbitrary code. The vendor has not released a patch despite early disclosure notification.

Vendors: [Fast](https://junglewise.ai/threats/vendors/fast).

## Quick answers

**Is CVE-2026-101039 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-101039 being exploited in the wild.

**How severe is CVE-2026-101039?** Critical severity, with a CVSS score of 10, published 28 September 2026.

**Which products and versions are affected?** Fast FAC1900R 20190827_2.0.2.

**Is there a fix for CVE-2026-101039?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-101039 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-101039?** Check whether you run Fast FAC1900R 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

The copy_msg_element function in the devdiscover service processes UDP packets on port 5001 but fails to validate the length field before calling memcpy, allowing a user-controlled length value up to 65535 bytes to overflow a ~229-byte stack buffer. The vulnerability is triggered via a network-accessible UDP service with no authentication required, and can overwrite the return address to achieve code execution or service crash. No official patch has been released.

## Affected products

- FAST FAC1900R 20190827_2.0.2

## Timeline

- 2026-09-28: disclosed: Published to NVD
- 2026-09-28: other: Exploit proof-of-concept publicly available on GitHub

## References

- [https://github.com/xiaobor123/vuls-find-VxWorks/tree/main/vul-find-FAST_FAC1900R-copy_msg_element(2)](https://github.com/xiaobor123/vuls-find-VxWorks/tree/main/vul-find-FAST_FAC1900R-copy_msg_element(2))
- [https://vuldb.com/cve/CVE-2026-101039](https://vuldb.com/cve/CVE-2026-101039)

## Related threats

- [Fast FAC1900R stack-based buffer overflow in uhttpd](https://junglewise.ai/threats/cve-2026-96676-a-vulnerability-was-identified-in-fast-fac1900r-20190827-2-0-2)