A malicious client which is allowed to send very large amounts of traffic (billions of packets) to a DHCP server can eventually overflow a 32-bit reference counter, potentially causing dhcpd to crash.

Versions of DHCP affected: 4.1.0 -> 4.1-ESV-R15, 4.2.0 -> 4.2.8, 4.3.0 -> 4.3.6, 4.4.0

ISC DHCP 4.1.x before 4.1-ESV-R13 and 4.2.x and 4.3.x before 4.3.4 does not restrict the number of concurrent TCP sessions, which allows remote attackers to cause a denial of service (INSIST assertion failure or request-processing outage) by establishing many sessions.

The server in ISC DHCP 3.x and 4.x before 4.2.2, 3.1-ESV before 3.1-ESV-R3, and 4.1-ESV before 4.1-ESV-R3 allows remote attackers to cause a denial of service (daemon exit) via a crafted DHCP packet.

The server in ISC DHCP 3.x and 4.x before 4.2.2, 3.1-ESV before 3.1-ESV-R3, and 4.1-ESV before 4.1-ESV-R3 allows remote attackers to cause a denial of service (daemon exit) via a crafted BOOTP packet.

dhclient in ISC DHCP 3.0.x through 4.2.x before 4.2.1-P1, 3.1-ESV before 3.1-ESV-R1, and 4.1-ESV before 4.1-ESV-R2 allows remote attackers to execute arbitrary commands via shell metacharacters in a hostname obtained from a DHCP message, as demonstrated by a hostname that is provided to dhclient-script.

Multiple memory leaks in ISC DHCP 4.1.x and 4.2.x before 4.2.4-P1 and 4.1-ESV before 4.1-ESV-R6 allow remote attackers to cause a denial of service (memory consumption) by sending many requests.

ISC DHCP 4.1.x before 4.1-ESV-R7 and 4.2.x before 4.2.4-P2 allows remote attackers to cause a denial of service (daemon crash) in opportunistic circumstances by establishing an IPv6 lease in an environment where the lease expiration time is later reduced.