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Vulnerability record · CVE-2026-40854 · published 16 September 2026

CVE-2026-40854: Authentication bypass by spoofing vulnerability

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

8.7 CVSS 4.0 High EPSS 0.32% · top 77.7% CWE-290 · Authentication bypass by spoofing Awaiting Analysis
8.7CVSS 4.0 base score
0.32%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
1References
16 Sep 2026Last modified by NVD

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

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

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

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Source: NIST National Vulnerability Database (record CVE-2026-40854), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.