protocols/jabber/auth.c in libpurple in Pidgin 2.6.0, and possibly other versions, does not follow the "require TLS/SSL" preference when connecting to older Jabber servers that do not follow the XMPP specification, which causes libpurple to connect to the server without the expected encryption and allows remote attackers to sniff sessions.
Exploitability
AV:NAC:LAu:NImpact
C:PI:NA:N5/AV:N/AC:L/Au:N/C:P/I:N/A:N