cache.c in ircd-ratbox before 2.2.9 allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a HELP command.
A Denial of Service vulnerability exists in ircd-ratbox 3.0.9 in the MONITOR Command Handler.
modules/m_capab.c in (1) ircd-ratbox before 3.0.8 and (2) Charybdis before 3.4.2 does not properly support capability negotiation during server handshakes, which allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a malformed request.
Non-registered IRC users using (1) ircd-hybrid 7.0.1 and earlier, (2) ircd-ratbox 1.5.1 and earlier, or (3) ircd-ratbox 2.0rc6 and earlier do not have a rate-limit imposed, which could allow remote attackers to cause a denial of service by repeatedly making requests, which are slowly dequeued.