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CVE-2026-40854

Session auth bypass via cookie value in T-Mobile 5G Box IDU routers

CVSS 4.0 8.7 HIGHCheck source for fixed versionsKEV status unknown
Original advisory

cve-program · CVE-2026-40854

Published

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

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Affected versions, risk and source history

Exploitation and risk

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cve-program · CVE-2026-40854

Published

Session auth bypass via cookie value in T-Mobile 5G Box IDU routers

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 published
16 Sep 2026 11:21:10 UTC
Source modified
16 Sep 2026 17:41:03 UTC
Saved here
23 Oct 2026 15:48:27 UTC
Source terms
CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 4.0 · 8.7 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

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Sources read 13 Nov 10:02 UTC · 274 of 275 readable · 272 fully read · documentation 469/469 current

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