# CVE-2026-40857: CSRF token bypass in T-Mobile 5G Box IDU routers

> Remote attackers can perform unauthorized actions on T-Mobile 5G Box IDU routers by bypassing CSRF token validation via a malicious website.

- **Severity:** High 8.4 (`CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 16 Sep 2026
- **Updated:** 16 Sep 2026
- **Also known as:** GHSA-6v9q-56wf-hqwp

## What is CVE-2026-40857?

CVE-2026-40857 is a high-severity vulnerability in WNC T-Mobile 5G Box IDU, published on 16 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

WNC T-Mobile 5G Box IDU router contains a cross-site request forgery (CSRF) vulnerability in the portal.cgi component. The anti-CSRF mechanism fails to validate the csrf_token_value parameter, accepting any arbitrary value as valid. This allows a remote attacker to perform unauthorized actions on the device by tricking an authenticated user into visiting a malicious website.This issue has been fixed in firmware version 1.1.0.651412

Weakness: CWE-352 (Cross-Site Request Forgery)

## Which versions are affected by CVE-2026-40857?


## How do I fix CVE-2026-40857?

No fix has been published for CVE-2026-40857 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-40857 being exploited?

There is no known exploitation of CVE-2026-40857 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40857 and fix it if it is affected.

What it is: CVE-2026-40857 is a high-severity vulnerability in WNC T-Mobile 5G Box IDU, published on 16 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-40857 in the wild and no public exploit code.

Affected product: WNC T-Mobile 5G Box IDU. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-40857/ (Markdown: https://insights.sbomify.com/CVE-2026-40857/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40857
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40857
- OSV: https://osv.dev/vulnerability/CVE-2026-40857

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-40857/
Summaries are generated and may contain mistakes; the official description above is the record.