title: An option refcount overflow exists in dhcpd
description: In ISC DHCP 4.4.0 -> 4.4.3, ISC DHCP 4.1-ESV-R1 -> 4.1-ESV-R16-P1, when the function option_code_hash_lookup() is called from add_option(), it increases the option's refcount field. However, there is not a corresponding call to option_dereference() to decrement the refcount field. The function add_option() is only used in server responses to lease query packets. Each lease query response calls this function for several options, so eventually, the reference counters could overflow and cause the server to abort.
problem types: A DHCP server configured with allow leasequery;, a remote machine with access to the server can send lease queries for the same lease multiple times, leading to the add_option() function being repeatedly called. This could cause an option's refcount field to overflow and the server to abort. Internally, reference counters are integers and thus overflow at 2^31 references, so even at 1000 lease query responses per second, it would take more than three weeks to crash the server. Affects In ISC DHCP 4.4.0 -> 4.4.3, ISC DHCP 4.1-ESV-R1 -> 4.1-ESV-R16-P1
affected:
{
vendor: ISC
product: ISC DHCP
versions:
version: 4.4.0 through versions before 4.4.3-P1, status: affected
version: 4.1 ESV 4.1-ESV-R1 through versions before 4.1-ESV-R16-P1, status: affected
}
metrics:
cvssV3_1: [
version: 3.1
vectorString: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
attackVector: ADJACENT_NETWORK
attackComplexity: LOW
privilegesRequired: NONE
userInteraction: NONE
scope: UNCHANGED
confidentialityImpact: NONE
integrityImpact: NONE
availabilityImpact: HIGH
baseScore: 6.5
baseSeverity: MEDIUM
]
exploits: We are not aware of any active exploits.
solutions: Upgrade to the patched release most closely related to your current version of ISC DHCP. These can all be downloaded from https://www.isc.org/downloads.  4.4.3-P1 4.1-ESV-R16-P2
workarounds: Disable lease query on the server for DHCPv4 or restart the server periodically.