Facebook mailto injection leads to social engineering & spam attack

Rahul Kankrale
Feb 3, 2018 · 1 min read

Facebook mobile sites: m.facebook & mbasic.facebook provide lite tag to friends feature.

when you goes to tag friends list open for selection and there is Cancel button .

when you see at url of this feature there is cancel_uri parameter which link to previous url of page.

I modified this parameter to openredirect but cant able todo as linkshim protection so i tried another protocol rather than HTTP, like :

mailto, whatsapp, fb, twitter etc.

and all are accepted, then i passed with mailto protocol with all its parameters (reciever email,subject,body, attachment) and all are injectable., and link injected behind Cancel button.

Once victim got this crafted url and when he click on cancel button his email client will open with prefilled data(inserted by attacker) which trick victim to submit his credential using some social engineering techniques.

Final POC url:


  • Reported to facebook
  • Accepted risk with no bounty as social engineering involved.
  • Closed report without fix.

Point to be noted :

  • H1 also accepted same as parameter injection.


Rahul Kankrale

Suggestion require for mailto exploit for such a issue : Rahul Kankrale

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