CVE-2026-40857: CSRF token bypass in T-Mobile 5G Box IDU routers

Severity: high (CVSS 8.4 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-16 · updated 2026-09-28
Weakness: CWE-352

Description

WNC T-Mobile 5G Box IDU router contains a cross-site request forgery (CSRF) vulnerability in the portal.cgi component. The anti-CSRF mechanism fails to validate the csrf_token_value parameter, accepting any arbitrary value as valid. This allows a remote attacker to perform unauthorized actions on the device by tricking an authenticated user into visiting a malicious website.This issue has been fixed in firmware version 1.1.0.651412

Affected products

WNC T-Mobile 5G Box IDU: before 1.1.0.651412 — fixed in 1.1.0.651412

How to fix

Upgrade to a fixed version: WNC T-Mobile 5G Box IDU 1.1.0.651412. Check the vendor advisory for mitigations.

References

https://cert.pl/posts/2026/09/CVE-2026-40854

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