# CVE-2026-40856: WNC T-Mobile 5G Box IDU improper access control in wnc_maccheck.cgi

Source: https://junglewise.ai/threats/cve-2026-40856-wnc-t-mobile-5g-box-idu-improper-access-control-in-wnc-maccheck  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-16. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-40856 · Severity: info · Published 2026-09-16

The WNC T-Mobile 5G Box IDU is a wireless router used by T-Mobile customers to provide 5G connectivity. A vulnerability in the wnc_maccheck.cgi endpoint allows an unauthenticated remote attacker to retrieve sensitive configuration data, including administrator passwords, WiFi passphrases, and device technical information. This could lead to unauthorized access to the router's administrative panel and WiFi network compromise.

Technologies: [WNC T-Mobile 5G Box IDU](https://junglewise.ai/threats/technologies/t-mobile-5g-box-idu). Vendors: [WNC](https://junglewise.ai/threats/vendors/wnc).

## Quick answers

**Is CVE-2026-40856 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-40856 being exploited in the wild.

**How severe is CVE-2026-40856?** Informational severity, published 16 September 2026.

**Which products and versions are affected?** WNC T-Mobile 5G Box IDU before 1.1.0.651412.

**Is there a fix for CVE-2026-40856?** A patch was published on 2026-09-16: Fixed in firmware version 1.1.0.651412 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-40856 attacked?** It is attacked over the network, in device firmware.

**Am I affected by CVE-2026-40856?** Check whether you run WNC T-Mobile 5G Box IDU 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 vulnerability is a missing authentication for critical function (CWE-306) in the wnc_maccheck.cgi endpoint of WNC T-Mobile 5G Box IDU firmware. The endpoint is accessible without any authentication mechanism and exposes sensitive configuration data via unauthenticated requests. A remote attacker on the network can directly query this endpoint to retrieve administrative credentials, WiFi passphrases, and device configuration information. The attack requires network reachability to the router but no prior authentication or credentials. This issue has been patched in firmware version 1.1.0.651412 and earlier versions are vulnerable.

## Affected products

- WNC T-Mobile 5G Box IDU before 1.1.0.651412

## Timeline

- 2026-09-16: disclosed
- 2026-09-16: patched: Fixed in firmware version 1.1.0.651412

## References

- [https://cert.pl/posts/2026/09/CVE-2026-40854](https://cert.pl/posts/2026/09/CVE-2026-40854)

## Related threats

- [WNC T-Mobile 5G Box IDU OS command injection in password change](https://junglewise.ai/threats/cve-2026-58147-wnc-t-mobile-5g-box-idu-os-command-injection-in-password-change)
- [WNC T-Mobile 5G Box IDU OS command injection in portal.cgi](https://junglewise.ai/threats/cve-2026-58146-wnc-t-mobile-5g-box-idu-os-command-injection-in-portal-cgi)
- [WNC T-Mobile 5G Box IDU CSRF in portal.cgi](https://junglewise.ai/threats/cve-2026-40857-wnc-t-mobile-5g-box-idu-csrf-in-portal-cgi)
- [WNC T-Mobile 5G Box IDU command injection in ping functionality](https://junglewise.ai/threats/cve-2026-40855-wnc-t-mobile-5g-box-idu-command-injection-in-ping-functionality)
- [WNC T-Mobile 5G Box IDU authentication bypass in portal.cgi](https://junglewise.ai/threats/cve-2026-40854-wnc-t-mobile-5g-box-idu-authentication-bypass-in-portal-cgi)