CVE-2023-36842 in Junos OS
Summary
by MITRE • 01/12/2024
An Improper Check for Unusual or Exceptional Conditions vulnerability in Juniper DHCP Daemon (jdhcpd) of Juniper Networks Junos OS allows an adjacent, unauthenticated attacker to cause the jdhcpd to consume all the CPU cycles resulting in a Denial of Service (DoS).
On Junos OS devices with forward-snooped-client configured, if an attacker sends a specific DHCP packet to a non-configured interface, this will cause an infinite loop. The DHCP process will have to be restarted to recover the service.
This issue affects:
Juniper Networks Junos OS
* All versions earlier than 20.4R3-S9; * 21.2 versions earlier than 21.2R3-S7; * 21.3 versions earlier than 21.3R3-S5; * 21.4 versions earlier than 21.4R3-S5; * 22.1 versions earlier than 22.1R3-S4; * 22.2 versions earlier than 22.2R3-S3; * 22.3 versions earlier than 22.3R3-S2; * 22.4 versions earlier than 22.4R2-S2, 22.4R3; * 23.2 versions earlier than 23.2R2.
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Analysis
by VulDB Data Team • 01/12/2024
The vulnerability CVE-2023-36842 represents a critical improper check for unusual or exceptional conditions flaw within Juniper Networks' DHCP daemon (jdhcpd) component of Junos OS. This weakness stems from inadequate input validation and error handling mechanisms that fail to properly process malformed or unexpected DHCP packets. The vulnerability specifically manifests when forward-snooped-client functionality is configured on the device, creating a condition where legitimate network traffic can trigger abnormal processing behavior. The root cause lies in the daemon's failure to validate incoming DHCP packets against expected protocols and configurations, leading to an exploitable state where malicious input can cause system resources to be consumed excessively.
The technical exploitation of this vulnerability occurs through a targeted attack vector that requires an adjacent, unauthenticated attacker to send a specifically crafted DHCP packet to a non-configured interface on the affected device. When such a packet is received, the jdhcpd process enters an infinite loop due to the lack of proper boundary checking and conditional validation. This condition causes the daemon to continuously process the malformed packet without proper termination conditions, resulting in 100% CPU utilization and complete service disruption. The infinite loop behavior directly violates the principle of bounded execution and demonstrates a classic example of a resource exhaustion attack pattern that can be classified under CWE-703 - Improper Check or Handling of Exceptional Conditions. The attack does not require authentication or network privileges beyond local network access, making it particularly dangerous for network infrastructure devices.
The operational impact of this vulnerability extends beyond simple service disruption to encompass complete network availability compromise. Affected devices become unusable for DHCP services, potentially affecting network connectivity for all devices relying on dynamic IP assignment. The recovery process requires manual intervention including daemon restart procedures, which can cause extended downtime and service interruption. Network administrators must perform immediate remediation actions including applying security patches or upgrading to patched versions of Junos OS. The vulnerability affects multiple software release lines across different major versions, indicating a widespread issue that requires coordinated patch management across the entire Juniper OS ecosystem. Organizations with extensive Juniper network deployments face significant operational challenges in identifying and remediating all affected devices simultaneously.
Mitigation strategies for this vulnerability include immediate deployment of vendor-provided patches and firmware updates for all affected Junos OS versions. Network administrators should also implement network segmentation and access controls to limit adjacent network access to critical devices. The configuration of forward-snooped-client should be carefully reviewed and restricted to only necessary interfaces to minimize attack surface. Monitoring and alerting systems should be enhanced to detect unusual CPU utilization patterns and potential DoS conditions. This vulnerability aligns with ATT&CK technique T1499.004 - Endpoint Denial of Service, which specifically addresses resource exhaustion attacks targeting system services. Organizations should also consider implementing network-based intrusion detection systems to identify and block suspicious DHCP packet patterns, and establish incident response procedures for rapid remediation of similar vulnerabilities. The vulnerability highlights the importance of proper input validation and error handling in network service daemons, emphasizing the need for robust defensive programming practices throughout the software development lifecycle.