SSL stripping

term

security

Keeping a victim on plain HTTP by rewriting the links that would have taken them to HTTPS, while the attacker speaks HTTPS to the real server.

Presented by Moxie Marlinspike in 2009, the technique exploited the fact that users almost never type the scheme: they arrive at a site over plain HTTP and are redirected, or they follow a link. An attacker in the path rewrites those redirects and links so the victim's side of the conversation is never encrypted at all, while the attacker's side to the server is - so the server sees a normal secure session and the victim sees a page that simply lacks a padlock nobody was looking for. It required no invalid certificate and produced no warning, which is what made it effective. HTTP Strict Transport Security is the direct answer: a site instructs the browser to use HTTPS for that name for a stated period, so there is no plain-text first request to intercept, and preload lists carry the instruction before the first visit. The technique is largely historical for major sites and remains relevant wherever a redirect from plain HTTP is still the entry point.

Also known as: ssl strip, sslstrip, https downgrade

Sources

Moxie Marlinspike, New Tricks for Defeating SSL in Practice, Black Hat DC 2009: the technique intercepts HTTP traffic and rewrites HTTPS links so the victim never initiates a secure connection, while the attacker maintains one with the server

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