Design document functions which receive a user http request object may expose authorization or session cookie headers of the user who accesses the document.
These design document functions are: * list * show * rewrite * update
An attacker can leak the session component using an HTML-like output, insert the session as an external resource (such as an image), or store the credential in a _local document with an "update" function.
For the attack to succeed the attacker has to be able to insert the design documents into the database, then manipulate a user to access a function from that design document.
Workaround: Avoid using design documents from untrusted sources which may attempt to access or manipulate request object's headers