CVE-2026-40854
HIGHDescription
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
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v4 Vector
Exploitability
Impact
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:X/V:X/RE:X/U:X
Exploit Intelligence
EPSS data unavailable for this CVE.
References
Related Vulnerabilities
Other CWE-290 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2024-4358 | Critical | 9.8 | 97% | KEV | - |
| CVE-2022-24112 | Critical | 9.8 | 96% | KEV | Fix |
| CVE-2022-23131 | Critical | 9.1 | 96% | KEV | - |
| CVE-2021-29441 | High | 8.6 | 88% | - | Fix |
| CVE-2019-1234 | High | 7.5 | 75% | - | - |
| CVE-2021-31195 | Medium | 6.5 | 74% | - | Fix |
Common questions
How do I fix CVE-2026-40854?
No published fix for CVE-2026-40854 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
How severe is CVE-2026-40854?
CVE-2026-40854 has a CVSS v4 base score of 8.7, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-16.