util.xml: Do not allow doctypes, comments or processing instructions
Yes. This is as bad as it sounds. CVE pending.
In Prosody itself, this only affects mod_websocket, which uses util.xml
to parse the <open/> frame, thus allowing unauthenticated remote DoS
using Billion Laughs. However, third-party modules using util.xml may
also be affected by this.
This commit installs handlers which disallow the use of doctype
declarations and processing instructions without any escape hatch. It,
by default, also introduces such a handler for comments, however, there
is a way to enable comments nontheless.
This is because util.xml is used to parse human-facing data, where
comments are generally a desirable feature, and also because comments
are generally harmless.
No 'to' attribute:
IQ: Pass to appropriate handler
Presence: Broadcast to contacts
- if initial presence, also send out presence probes
- if probe would be to local user, generate presence stanza for them
Message: Route as if it is addressed to the bare JID of the sender
To a local host:
IQ: Pass to appropriate handler
Presence: -
Message: Deliver to admin?
To local contact:
Bare JID:
IQ: Pass to appropriate handler
Presence: Broadcast to all resources
Message: Route to 'best' resource
Full JID:
IQ: Send to resource
Presence: Send to resource
Message: Send to resource
Full JID but resource not connected:
IQ: Return service-unavailable
Message: Handle same as if to bare JID
Presence: Drop (unless type=subscribe[ed])
To remote contact:
Initiate s2s connection if necessary
Send stanza across