CVE-2022-2928 in DHCPD
Summary
by MITRE • 10/07/2022
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.
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Analysis
by VulDB Data Team • 11/15/2024
The vulnerability described in CVE-2022-2928 represents a critical memory management flaw within ISC DHCP server versions ranging from 4.4.0 through 4.4.3 and 4.1-ESV-R1 through 4.1-ESV-R16-P1. This issue manifests as a memory leak through improper reference counting mechanisms within the dhcp server's option handling code. The flaw specifically occurs in the option_code_hash_lookup() function when invoked from add_option(), creating a scenario where option reference counters are incremented but never properly decremented. This fundamental design error stems from the absence of corresponding option_dereference() calls that would normally balance the increment operations performed by option_code_hash_lookup().
The technical implementation of this vulnerability operates through a cascading reference counting mechanism that ultimately leads to resource exhaustion. When lease query packets are processed by the dhcp server, the add_option() function is invoked multiple times for various options within each response. Each invocation of this function triggers the increment of an option's refcount field without a corresponding decrement operation. This creates a memory leak where reference counters continue to increase indefinitely with each processed lease query response. The cumulative effect of these unbalanced reference counts eventually leads to integer overflow conditions that cause the server process to terminate abruptly, resulting in a denial of service condition.
The operational impact of this vulnerability extends beyond simple service disruption to create a potential attack vector for denial of service attacks against dhcp infrastructure. Attackers could exploit this weakness by repeatedly sending lease query packets to target dhcp servers, causing progressive memory consumption until the server crashes. The vulnerability affects the server's ability to process legitimate dhcp requests and responses, potentially disrupting network operations for extended periods. The specific context of this flaw being limited to lease query responses means that it primarily impacts environments where dhcp servers must handle query operations from clients or other dhcp servers, making it particularly dangerous in enterprise and network infrastructure environments.
From a cybersecurity perspective, this vulnerability aligns with CWE-404, which describes improper resource management, specifically focusing on memory leaks and reference counting errors. The flaw demonstrates characteristics consistent with the ATT&CK technique T1499.004, which involves network denial of service attacks through resource exhaustion. The vulnerability's exploitation requires minimal privileges and can be executed remotely, making it particularly attractive to attackers seeking to disrupt network services. Organizations utilizing affected ISC DHCP versions face significant risk of service interruptions, especially in environments where dhcp servers handle frequent lease query operations. The root cause analysis reveals a fundamental flaw in the server's memory management architecture that fails to maintain proper reference counting balance, creating an exploitable condition that can be amplified through repeated attack vectors.
The recommended mitigation strategy involves immediate deployment of patched versions of ISC DHCP software that address the reference counting imbalance in the option handling code. Organizations should prioritize updating their dhcp server infrastructure to versions that contain the fix for this vulnerability. Additionally, implementing network monitoring solutions that can detect unusual patterns of lease query traffic may help identify potential exploitation attempts. The fix typically involves ensuring that every increment operation in the option_code_hash_lookup() function has a corresponding decrement operation through proper option_dereference() calls. System administrators should also consider implementing access controls and rate limiting on dhcp query operations to reduce the impact of potential exploitation attempts while awaiting patch deployment.