Quassel through 0.13.1, when --require-ssl is enabled, launches without SSL or TLS support if a usable X.509 certificate is not found on the local system.

The onReadyRead function in core/coreauthhandler.cpp in Quassel before 0.12.4 allows remote attackers to cause a denial of service (NULL pointer dereference and crash) via invalid handshake data.

The CoreUserInputHandler::doMode function in core/coreuserinputhandler.cpp in Quassel 0.10.0 allows remote attackers to cause a denial of service (application crash) via the "/op " command in a query.

Quassel before 0.12.2 does not properly re-initialize the database session when the PostgreSQL database is restarted, which allows remote attackers to conduct SQL injection attacks via a \ (backslash) in a message. NOTE: this vulnerability exists because of an incomplete fix for CVE-2013-4422.

Quassel before 0.12-rc1 uses an incorrect data-type size when splitting a message, which allows remote attackers to cause a denial of service (crash) via a long CTCP query containing only multibyte characters.

Stack consumption vulnerability in the message splitting functionality in Quassel before 0.12-rc1 allows remote attackers to cause a denial of service (uncontrolled recursion) via a crafted massage.

The blowfishECB function in core/cipher.cpp in Quassel IRC 0.10.0 allows remote attackers to cause a denial of service (out-of-bounds read) via a malformed string.

SQL injection vulnerability in Quassel IRC before 0.9.1, when Qt 4.8.5 or later and PostgreSQL 8.2 or later are used, allows remote attackers to execute arbitrary SQL commands via a \ (backslash) in a message.

The CtcpParser::packedReply method in core/ctcpparser.cpp in Quassel before 0.7.3 allows remote attackers to cause a denial of service (crash) via a crafted Client-To-Client Protocol (CTCP) request, as demonstrated in the wild in September 2011.