Individual skill
testing-for-email-header-injection
Test web application email functionality for SMTP header injection vulnerabilities that allow attackers to inject additional email headers, modify recipients, and abuse contact forms for spam relay.
internal/tools/skills/data/web-application-security/testing-for-email-header-injection/SKILL.md
Source commit d42f381ad34843e71a42658e5c57290c713e85af
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- Observed behavior
- Not checked yet
- Last checked
- Nov 7, 2026
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- Repository last updated
- Nov 7, 2026
- License
- Apache-2.0
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- cybersecurity Repository topic
- security Repository topic
- bug-bounty Repository topic
- automation Repository topic
- autonomous-pentesting Repository topic
- ai-agent Repository topic
- ai-security Repository topic
- ethical-hacking Repository topic
- golang Repository topic
- penetration-testing Repository topic
- email-injection Declared skill tag
- smtp-injection Declared skill tag
- crlf-injection Declared skill tag
- header-injection Declared skill tag
- spam-relay Declared skill tag
- contact-form Declared skill tag
- email-security Declared skill tag
- testing Derived category
- security Derived category
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# Testing for Email Header Injection
## When to Use
- When testing contact forms, feedback forms, or "email a friend" functionality
- During assessment of password reset email functionality
- When testing newsletter subscription or notification email systems
- During penetration testing of applications that send emails based on user input
- When auditing email-related API endpoints for header injection
### How to CONFIRM a Hit (avoid false negatives)
- **Positive signal**: an injected CRLF actually adds a header or recipient that takes effect — a copy of the email lands in your attacker-controlled (e.g. agentmail) inbox via injected `Cc`/`Bcc`, or `From`/`Reply-To` is overridden in the delivered message.
- Confirm by inspecting the **raw source / "Show Original"** of a RECEIVED email for your injected `Cc:`, `Bcc:`, `From:`, `Reply-To:`, or overridden body — do not rely on the form returning success.
- An HTTP 200 from the form is NOT a hit (the app may strip newlines); a single failed payload is NOT a clean negative until encodings and fields are varied.