Privilege escalation: User is able to add a page to his watchlist without having the permission

Szenario:

create user1 and user2
user1 has access to space1
user2 has access to space2

user1 can add a page to his watchlist by manipulating (using a proxy like webscarab) the postrequest to
http://localhost:8080/dwr/exec/PageNotification.startWatching.dwr

and replacing the id contained in parameter c0-param0

the posted data looks like that

callCount=1
c0-scriptName=PageNotification
c0-methodName=startWatching
c0-id=215_1221492126248
c0-param0=string:393224
xml=true

This results in the page being added to the users watchlist, displaying the title and the corresponding space, even though the user should not have access to this space at all.

I have not tested the email functionality since there was no mailserver available for testing wether a message gets sent on change of the watched page.

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