# DNS Rebinding Vulnerability

> Detects server-side host validation logic vulnerable to DNS rebinding attacks, allowing attackers to bypass IP-based restrictions.

- Skill: `zakirkun/dns-rebinding-vulnerability` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add zakirkun/dns-rebinding-vulnerability`
- Raw SKILL.md: https://api.skillmd.com/api/skills/zakirkun/dns-rebinding-vulnerability/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: zakirkun (https://skillmd.com/u/zakirkun)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/zakirkun/dns-rebinding-vulnerability

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# DNS Rebinding Vulnerability

## Overview
DNS rebinding allows an attacker to bypass Same-Origin Policy and IP allowlists. The attack works by:
1. Victim visits attacker's page at `evil.com`
2. Attacker's DNS TTL expires; `evil.com` resolves to `127.0.0.1`
3. JavaScript makes requests to `evil.com` which now reach the victim's localhost services
4. Services that only check the IP (not the Host header) are bypassed

Vulnerable applications that check `Host` header or resolve hostname for validation without proper binding.

## Detection Strategy
- URL validation that checks hostname string rather than resolved IP
- HTTP servers binding to all interfaces without Host header validation
- SSRF protection based on DNS resolution rather than allowlist