A researcher has found a serious vulnerability in the Facebook platform that could allow hijacking anyone’s Facebook account. For discovering this OAuth Framework flaw, Facebook awarded a hefty bug bounty to the researcher.
Researcher Amol Baikar has found a serious OAuth Framework flaw affecting the Facebook platform.
Sharing his findings in a blog post, the researcher revealed that the bug existed in the “Login with Facebook” feature. Hence, it became possible for an adversary to hijack access tokens when a user would log in to other websites via Facebook. In turn, this would not only allow hacking Facebook accounts but would also give access to the respective third-party services.
While explaining the normal login flow the researcher stated,
Though, the endpoint was secure enough to prevent known login bypass strategies two important points made it possible to exploit the page proxy which further exposed the cross-domain communication. As stated by the researcher, these were,
Hence, the access_token would ‘leak to any origin’, and an adversary could then set up a new phone number for recovery.
While Facebook initially addressed this matter, the researcher found that the OAuth’s core endpoint “
/dialog/oauth/” continued to redirect to page proxy.
Here is a demonstration of the exploit: