Http4s: CookieJar middleware accepts arbitrary Set-Cookie domain

When processing a Set-Cookie from a response, the CookieJar client middleware trusts the server-supplied Domain attribute verbatim, with no check that it domain-matches the host that sent the cookie (RFC6265 §5.3 step 6) and no public suffix check. A malicious or compromised server can therefore plant a cookie for any domain in the cookie jar, which is subsequently set on the client's next request to that victim domain, enabling session fixation or overwriting security-relevant cookies.

Impact

Session fixation and overwrite of security-relevant cookies for arbitrary domains contacted by the same wrapped client.

Preconditions

• Application uses the CookieJar client middleware.
• Application contacts an attacker-controlled (or compromised) server using the same jar it uses for trusted hosts.

Workarounds

• Do not share a CookieJar across trusted and untrusted targets.

Note

This middleware still does not implement public suffix rejection.