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CVE-2026-40854— Session auth bypass via cookie value in T-Mobile 5G Box IDU routers

Quick assessment

Affected
WNC T-Mobile 5G Box IDU
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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. A

CVSS 8.7 · High
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I. Basic Information for CVE-2026-40854

Vulnerability Information
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Vulnerability Title
Session auth bypass via cookie value in T-Mobile 5G Box IDU routers
Source: CVE Program / CVE List V5
Vulnerability 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
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
使用欺骗进行的认证绕过
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
WNC T-Mobile 5G Box IDU 0 ~ 1.1.0.651412 -

II. Public POCs for CVE-2026-40854

# POC Description Source Link Shenlong Link
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III. Intelligence Information for CVE-2026-40854

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Security Blog Posts for CVE-2026-40854 (1)

Same Patch Batch · WNC · 2026-09-16 · 6 CVEs total

CVE-2026-58146 9.4 CRITICAL Unauthorized remote code execution in T-Mobile 5G Box IDU routers
CVE-2026-58147 9.3 CRITICAL Authorized remote code execution via password change functionality in T-Mobile 5G Box IDU
CVE-2026-40855 9.3 CRITICAL Command Injection in T-Mobile 5G Box IDU router via ping functionality
CVE-2026-40857 8.4 HIGH CSRF token bypass in T-Mobile 5G Box IDU routers
CVE-2026-40856 7.1 HIGH Config disclosure in T-Mobile 5G Box IDU routers

IV. Related Vulnerabilities

Same product: T-Mobile 5G Box IDU
Same vendor: WNC
Same weakness: CWE-290

V. Comments for CVE-2026-40854

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