Quick answers
- Is CVE-2026-40854 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-40854 being exploited in the wild.
- How severe is CVE-2026-40854?
- Informational severity, with a CVSS score of 7.5, published 16 September 2026.
- Which products and versions are affected?
- WNC T-Mobile 5G Box IDU All versions before 1.1.0.651412.
- Is there a fix for CVE-2026-40854?
- 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-2026-40854 attacked?
- It is attacked over the network, in a network appliance.
- Am I affected by CVE-2026-40854?
- 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
CVE-2026-40854 is an authentication bypass vulnerability in the portal.cgi component of the WNC T-Mobile 5G Box IDU router. The session verification mechanism fails to properly validate the sessionid cookie; it only checks for the existence of a corresponding file in /tmp/login_user, allowing attackers to bypass authentication by injecting directory traversal sequences (e.g., "." or "..") into the cookie value. No authentication is required—the attack is network-accessible. A successful exploit grants an unauthenticated attacker full access to the device's administrative panel and configuration. The vulnerability was fixed in firmware version 1.1.0.651412.
Affected products
- WNC T-Mobile 5G Box IDU All versions before 1.1.0.651412
Timeline
- 2026-09-16: disclosed
- 2026-09-16: patched: Fixed in firmware version 1.1.0.651412