CVE Intelligence
High Authentication

CVE-2026-40854 — 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

Published Sep 16, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: CERT-PL

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • Technical severity (high)+6

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
—
No EPSS score.
Affects
WNC
T-Mobile 5G Box IDU
CVSS base
8.7
High · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Total
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (WNC T-Mobile 5G Box IDU).
  2. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  3. Search available logs for exploit probes matching the vulnerability class (authentication), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
WNC T-Mobile 5G Box IDU < 1.1.0.651412 Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Adjacent
Attack complexity
Low
Attack requirements
None
Privileges required
None
User interaction
None
Scope
X
Confidentiality (vulnerable system)
High
Integrity (vulnerable system)
High
Availability (vulnerable system)
High
Confidentiality (subsequent)
None
Integrity (subsequent)
None
Availability (subsequent)
None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
8.7 CVSS 4.0 High — — cvd@cert.pl via NIST National Vulnerability Database
8.7 CVSS 4.0 High — — CERT-PL via CVE Program (cve.org) e CISA ADP
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 (score shown at the top: cvd@cert.pl)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-290 · Authentication Bypass by Spoofing

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Review authentication logs: logins without MFA, anomalous sessions and recently created accounts.
authentication logs

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · wnc/t-mobile 5g box idu
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 15, 2026
  • CVSS changed · 8.7
    Oct 15, 2026 · NIST National Vulnerability Database
  • Source status changed · → Awaiting Analysis
    Oct 15, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 15, 2026 · NIST National Vulnerability Database
  • CVE published
    Sep 16, 2026 · CERT-PL

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

1 on the record

Elsewhere on this site

WNC
every CVE for this vendor
Authentication
same class
CWE-290
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-58147 Authorized remote code execution via password change functionality in T-Mobile 5G Box IDU routers 29d
  • CVE-2026-58146 Unauthorized remote code execution in T-Mobile 5G Box IDU routers 29d
  • CVE-2026-40855 Command Injection in T-Mobile 5G Box IDU router via ping functionality 29d
  • CVE-2026-40856 Config disclosure in T-Mobile 5G Box IDU routers 29d
  • CVE-2026-40857 CSRF token bypass in T-Mobile 5G Box IDU routers 29d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No FIRST EPSS score.
  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-40854 is "Session auth bypass via cookie value in T-Mobile 5G Box IDU routers", rated High. It affects T-Mobile 5G Box IDU (WNC); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 8.7 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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