I haven’t really heard of many RealPlayer exploits, however this zero day one is a nasty. This is an Internet Explorer exploit only, so if you’re using FireFox you’re in luck.
October 19, 2007 (Computerworld) — Attackers are exploiting a zero-day vulnerability in RealPlayer in order to infect Windows machines running Internet Explorer, Symantec Corp. said late Thursday. The security company issued an alert that rated the threat with its highest possible score.
According to a warning issued to customers of its DeepSight threat network, Symantec said an ActiveX control installed by RealNetworks Inc.’s RealPlayer program is flawed. When combined with Microsoft Corp.’s Internet Explorer (IE) browser — which relies on ActiveX controls to extend its functionality — the bug can be exploited and malicious code downloaded to any PC that wanders to a specially crafted site.
Only systems on which both RealPlayer and IE have been installed are vulnerable.