Glossary of Security Terms: MitM

A Man-in-the-middle attack (MitM) intercepts a communication between two systems. For example, a Wi-Fi router can be compromised.

Comparing this to physical mail: If you're writing letters to each other, the mailman can intercept each letter you mail. They open it, read it, eventually modify it, and then repackage the letter and only then send it to whom you intended to sent the letter for. The original recipient would then mail you a letter back, and the mailman would again open the letter, read it, eventually modify it, repackage it, and give it to you. You wouldn't know there's a man in the middle in your communication channel – the mailman is invisible to you and to your recipient.

In physical mail and in online communication, MITM attacks are tough to defend. A few tips:

• Don't just ignore certificate warnings. You could be connecting to a phishing server or an imposter server.
• Sensitive sites without HTTPS encryption on public Wi-Fi networks aren't trustworthy.
• Check for HTTPS in your address bar and ensure encryption is in-place before logging in.

Learn more

• OWASP Article: Man-in-the-middle attack
• Wikipedia: Man-in-the-middle attack
• The 

  Public-Key-Pins

  header (HPKP) can significantly decrease the risk of MITM by instructing browsers to require a whitelisted certificate for all subsequent connections to that website.

View Previous Terms:

• Block cipher mode of operation
• Certificate authority
• Challenge-response authentication
• Cipher
• Cipher suite
• Ciphertext
• CORS
• CORS-safelisted request header
• CORS-safelisted response header
• Cross-site scripting
• Cryptanalysis
• Cryptographic hash function
• Cryptography
• CSP
• CSRF
• Decryption
• Digital certificate
• DTLS (Datagram Transport Layer Security)
• Encryption
• Forbidden header name
• Forbidden response header name
• Hash
• HMAC
• HPKP
• HSTS
• HTTPS
• Key
• OWASP
• Preflight request
• Public-key cryptography
• Reporting directive
• Robots.txt
• Same-origin policy
• Session Hijacking
• SQL Injection
• Symmetric-key cryptography
• TOFU
• Transport Layer Security (TLS)

Credits

• Source: https://developer.mozilla.org/en-US/docs/Glossary/MitM
• Published under Open CC Attribution ShareAlike 3.0 license