CVE-2026-40854
Session auth bypass via cookie value in T-Mobile 5G Box IDU routers
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
INFO
Published Date :
Sept. 16, 2026, 12:17 p.m.
Last Modified :
Sept. 28, 2026, 11:10 p.m.
Remotely Exploit :
No
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 4.0 | HIGH | 4bb8329e-dd38-46c1-aafb-9bf32bcb93c6 | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Update the router firmware to version 1.1.0.651412.
- Ensure session verification is properly implemented.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-40854.
| URL | Resource |
|---|---|
| https://cert.pl/posts/2026/09/CVE-2026-40854 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-40854 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-40854
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-40854 vulnerability anywhere in the article.
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cert.pl
Vulnerabilities in WNC T-Mobile 5G Box IDU routers
Vulnerabilities in WNC T-Mobile 5G Box IDU routers CVE ID CVE-2026-40854 Publication date 16 September 2026 Vendor WNC Product T-Mobile 5G Box IDU Vulnerable versions All before 1.1.0.651412 Vulnerabi ... Read more
The following table lists the changes that have been made to the
CVE-2026-40854 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Translated by [email protected]
Sep. 28, 2026
Action Type Old Value New Value Added Translation Title: T-Mobile 5G Box IDU de WNC, Description: El router WNC T-Mobile 5G Box IDU contiene una vulnerabilidad de omisión de autenticación en el componente portal.cgi. El mecanismo de verificación de sesión valida incorrectamente la cookie sessionid al verificar la existencia de un archivo correspondiente en /tmp/login_user. Un atacante puede omitir la autenticación utilizando entradas de directorio como '.' o '..' en la cookie, lo que permite el acceso no autorizado al panel de administración. Este problema ha sido solucionado en la versión de firmware 1.1.0.651412. -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Sep. 16, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-40854', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-09-16T17:40:01.238581Z'} -
New CVE Received by [email protected]
Sep. 16, 2026
Action Type Old Value New Value Added 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 Added CVSS V4.0 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 Added CWE CWE-290 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/40xxx/CVE-2026-40854.json">CVE-2026-40854</a> Added Reference https://cert.pl/posts/2026/09/CVE-2026-40854