CVE-2026-40854 — Session auth bypass via cookie value in T-Mobile 5G Box IDU routers

CVE-2026-40854

Session auth bypass via cookie value in T-Mobile 5G Box IDU routers PUBLISHED

Description (CNA)

WNC T-Mobile 5G Box IDU router contains an authentication bypass vulnerability in the portal.cgi component. The session verification mechanism improperly validates the sessionid cookie by checking for the existence of a corresponding file in /tmp/login_user. An attacker can bypass authentication by using directory entries such as "." or ".." in the cookie, allowing unauthorized access to the administration panel.This issue has been fixed in firmware version 1.1.0.651412

Affected (CNA)

Vendor / product	Versions
WNC / T-Mobile 5G Box IDU	affected 0 before 1.1.0.651412

CWE

CWE-290

References

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

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.