Use after free via shared cookies

Open Source Vulnerabilities CVE-2016-8623

A flaw was found in curl before version 7.51.0. The way curl handles cookies permits other threads to trigger a use-after-free leading to information disclosure.

Open Source Vulnerabilities CURL-CVE-2016-8623

libcurl explicitly allows users to share cookies between multiple easy handles that are concurrently employed by different threads. When cookies to be sent to a server are collected, the matching function collects all cookies to send and the cookie lock is released immediately afterwards. That function however only returns a list with *references* back to the original strings for name, value, path and so on. Therefore, if another thread quickly takes the lock and frees one of the original cookie structs together with its strings, a use after free can occur and lead to information disclosure. Another thread can also replace the contents of the cookies from separate HTTP responses or API calls.