unboundcompute/security-agent-skills · skills/testing-smtp-smuggling-and-email-spoofing/SKILL.md

testing-smtp-smuggling-and-email-spoofing skillA

testing-smtp-smuggling-and-email-spoofing is agent-read markdown (skill) from unboundcompute/security-agent-skills: Test a mail setup for sender spoofing that survives authentication: SPF, DKIM, and DMARC records that exist but do not align or enforce, subdomains left unprotected, and the end-of-data desync known as SMTP smuggling, where an inbound and an outbound mail server disagree on where one message ends so a second message with a forged, auth-passing sender is smuggled in. Covers policy present but not enforced, alignment gaps between the envelope and header sender, missing subdomain policy, open relay.

Indexed from public GitHub and served as immutable, content-addressed versions. Install it pinned to an exact SHA-256 with the mdr CLI, and every file is verified against the hash recorded here before it reaches your agent. The deterministic audit below grades the latest version, and the same file always earns the same grade.

How to install

Latest version
mdr add unboundcompute/security-agent-skills/testing-smtp-smuggling-and-email-spoofing@git:20260819.61df029
Exact content
mdr add unboundcompute/security-agent-skills/testing-smtp-smuggling-and-email-spoofing@sha256:017678ad065e0dd1

Pin to a label to follow the author's releases, or to a sha256 to freeze the exact bytes forever. Either way the resolved hash is written to mdr.lock, and mdr install reproduces it on any machine.

Badge

mdr badge

[![mdr](https://markdownregistry.com/badge/art_6fogzie7etko2zj3.svg)](https://markdownregistry.com/a/art_6fogzie7etko2zj3)

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Versions

versioncommittedcommitsizeaudit
git:20260819.61df029 latest2026-08-19 61df029 8,711 BA view

Audit of the latest version

A  17 of 17 checks passed. Deterministic, no model, same answer every run.
  • pass: Frontmatter block present
  • pass: Frontmatter declares a name
  • pass: Frontmatter declares a description
  • pass: Size between 200 bytes and 200 KB (8711 bytes)
  • pass: No zero-width or bidi control characters
  • pass: No instruction hidden inside an HTML comment
  • pass: No link to an exfiltration or paste host
  • pass: No credential-shaped string
  • pass: No instruction to send local credentials anywhere
  • pass: No text hidden with inline styles
  • pass: No prompt-injection phrasing
  • pass: No curl or wget piped into a shell
  • pass: No recursive delete of root, home or parent
  • pass: No instruction to read or print local credentials
  • pass: No base64 blob over 200 characters
  • pass: No link to a raw IP address
  • pass: No script tag

Source

GitHub

unboundcompute/security-agent-skills · 5 stars · license MIT · pushed 2026-09-08 · branch main

API

GET https://markdownregistry.com/api/v1/artifacts/art_6fogzie7etko2zj3
GET https://markdownregistry.com/api/v1/resolve?ref=unboundcompute/security-agent-skills/testing-smtp-smuggling-and-email-spoofing
GET https://markdownregistry.com/api/v1/blob/017678ad065e0dd13104c19f7ba44b758245c546fd56d3377a71dd3a6a175ab2

Agents talk at modelranch.com: hand yours the instructions there and it joins the network that reads files like this one.