# CVE-2021-4463: Longjing Technology BEMS API <= 1.21 Remote Arbitrary File Download

> Unauthenticated attackers can exploit path traversal in the downloads endpoint to read sensitive files from the server.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Nov 2025
- **Updated:** 14 May 2026
- **Also known as:** GHSA-4m64-g8r6-3ghw

## What is CVE-2021-4463?

CVE-2021-4463 is a high-severity path traversal vulnerability in Shenzhen Longjing Technology Co. Ltd. BEMS API, published on 12 Nov 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Longjing Technology BEMS API versions up to and including 1.21 contains an unauthenticated arbitrary file download vulnerability in the 'downloads' endpoint. The 'fileName' parameter is not properly sanitized, allowing attackers to craft traversal sequences and access sensitive files outside the intended directory.

Weakness: CWE-552 (Files or Directories Accessible to External Parties), CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2021-4463?


## How do I fix CVE-2021-4463?

No fix has been published for CVE-2021-4463 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-4463 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-4463 exists.

Public exploit code:

- Longjing Technology BEMS API 1.21 - Unauthenticated Arbitrary File Download (nuclei): http/cves/2021/CVE-2021-4463.yaml

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-4463 and fix it if it is affected.

What it is: CVE-2021-4463 is a high-severity path traversal vulnerability in Shenzhen Longjing Technology Co. Ltd. BEMS API, published on 12 Nov 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-4463 exists.

Affected product: Shenzhen Longjing Technology Co. Ltd. BEMS API. 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-2021-4463/ (Markdown: https://insights.sbomify.com/CVE-2021-4463/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-4463
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-4463
- OSV: https://osv.dev/vulnerability/CVE-2021-4463

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-4463/
Summaries are generated and may contain mistakes; the official description above is the record.