CVE-2026-40854 PUBLISHED

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

Assigner: CERT-PL
Reserved: 15.04.2026 Published: 16.09.2026 Updated: 16.09.2026

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

Metrics

CVSS 4.0

CVSS Vector: CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CVSS Score: 8.7

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Adjacent	Confidentiality	High	Confidentiality	None
Attack Complexity	Low	Integrity	High	Integrity	None
Attack Requirements	None	Availability	High	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

Product Status

Vendor	WNC
Product	T-Mobile 5G Box IDU
Versions	Default: unaffected affected from 0 to 1.1.0.651412 (excl.)

Credits

Patryk Bogdan finder
Adam Borczyk finder

References

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

Problem Types

CWE-290 Authentication bypass by spoofing CWE