CVE-2026-40854 Session auth bypass via cookie value in T-Mobile 5G Box IDU routers
Attackers can bypass authentication on T-Mobile 5G Box IDU routers by manipulating session cookies to access the administration panel.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-40854?
CVE-2026-40854 is a high-severity authentication bypass vulnerability in WNC T-Mobile 5G Box IDU, published on 16 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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
Weakness: CWE-290
Which versions are affected by CVE-2026-40854?
How do I fix CVE-2026-40854?
No fix has been published for CVE-2026-40854 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-40854 being exploited?
There is no known exploitation of CVE-2026-40854 in the wild and no public exploit code.
Sources
Also known as GHSA-7wq2-g42r-wr2h.