The MITRE CVE dictionary describes this issue as:
The silc_channel_message function in ops.c in the SILC protocol plugin in libpurple in Pidgin before 2.10.1 does not perform the expected UTF-8 validation on message data, which allows remote attackers to cause a denial of service (application crash) via a crafted message, a different vulnerability than CVE-2011-3594.
Find out more about CVE-2011-4603 from the
MITRE CVE dictionary dictionary and
Not vulnerable. This issue did not affect the version of pidgin as shipped with Red Hat Enterprise Linux 6 as it explicitly disables support for the SILC protocol.