CVE-2023-36839 in Junos OS
Summary
by MITRE • 10/25/2023
An Improper Validation of Specified Quantity in Input vulnerability in the Layer-2 control protocols daemon (l2cpd) of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated adjacent attacker who sends specific LLDP packets to cause a Denial of Service(DoS).
This issue occurs when specific LLDP packets are received and telemetry polling is being done on the device. The impact of the l2cpd crash is reinitialization of STP protocols (RSTP, MSTP or VSTP), and MVRP and ERP. Also, if any services depend on LLDP state (like PoE or VoIP device recognition), then these will also be affected.
This issue affects:
Juniper Networks Junos OS
* All versions prior to 20.4R3-S8; * 21.1 version 21.1R1 and later versions; * 21.2 versions prior to 21.2R3-S5; * 21.3 versions prior to 21.3R3-S4; * 21.4 versions prior to 21.4R3-S3; * 22.1 versions prior to 22.1R3-S2; * 22.2 versions prior to 22.2R3; * 22.3 versions prior to 22.3R2-S2; * 22.4 versions prior to 22.4R2;
Juniper Networks Junos OS Evolved
* All versions prior to 20.4R3-S8-EVO; * 21.1 version 21.1R1-EVO and later versions; * 21.2 versions prior to 21.2R3-S5-EVO; * 21.3 versions prior to 21.3R3-S4-EVO; * 21.4 versions prior to 21.4R3-S3-EVO; * 22.1 versions prior to 22.1R3-S2-EVO; * 22.2 versions prior to 22.2R3-EVO; * 22.3 versions prior to 22.3R2-S2-EVO; * 22.4 versions prior to 22.4R1-S1-EVO;
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Analysis
by VulDB Data Team • 10/25/2023
The vulnerability identified as CVE-2023-36839 represents a critical weakness in the Layer-2 control protocols daemon (l2cpd) of Juniper Networks Junos OS and Junos OS Evolved platforms. This issue stems from an improper validation of specified quantity in input, specifically concerning LLDP packets that are processed by the l2cpd component. The vulnerability is classified under CWE-20, which deals with improper input validation, and falls into the broader category of input validation flaws that can lead to various security consequences including denial of service conditions. The flaw is particularly concerning because it allows unauthenticated adjacent attackers to exploit the system through crafted LLDP packets, making it a significant threat in environments where physical access or network proximity can be achieved by malicious actors.
The technical exploitation of this vulnerability occurs when specific LLDP packets are received by the device while telemetry polling is active. This particular interaction triggers a crash within the l2cpd process, which subsequently results in the reinitialization of multiple spanning tree protocols including RSTP, MSTP, and VSTP, along with MVRP and ERP protocols. The cascading effect of this crash extends beyond simple daemon restart, as it affects fundamental network protocols that ensure proper layer-2 connectivity and loop prevention. From an operational perspective, this vulnerability represents a significant risk because it can disrupt network stability and availability, particularly in environments where these protocols are essential for maintaining network integrity. The attack vector is particularly dangerous as it requires only adjacent network access, meaning that an attacker positioned within the same network segment can potentially cause widespread disruption.
The operational impact of CVE-2023-36839 extends well beyond immediate service disruption, affecting critical network services that depend on LLDP state information. Network services such as Power over Ethernet (PoE) and Voice over IP (VoIP) device recognition rely heavily on LLDP for proper functioning, making the vulnerability particularly damaging in enterprise environments where these services are critical for network operations. When the l2cpd daemon crashes and restarts, it causes the reinitialization of spanning tree protocols which can lead to temporary network outages while the protocols reconverge. This disruption can be especially problematic in mission-critical environments where network availability is paramount, potentially causing cascading failures that affect multiple network services simultaneously.
Organizations affected by this vulnerability should prioritize immediate remediation through the application of Juniper's security patches and updates that address the input validation issue in the l2cpd component. The affected versions span multiple release branches of Junos OS and Junos OS Evolved, requiring careful inventory management and coordinated patch deployment across all impacted devices. Network administrators should also consider implementing network segmentation and access controls to limit adjacent network access where possible, as a defensive measure against exploitation attempts. Additionally, monitoring systems should be enhanced to detect unusual LLDP packet patterns that might indicate attempted exploitation of this vulnerability. From a compliance perspective, this vulnerability aligns with various security frameworks including NIST SP 800-53 and ISO 27001 requirements for vulnerability management and input validation controls. The ATT&CK framework would classify this vulnerability under T1499.004 for Network Denial of Service and potentially T1595.001 for Network Discovery, as exploitation requires understanding of network protocols and access to adjacent network segments. Organizations should also consider implementing intrusion detection systems that can identify malformed LLDP packets and alert on potential exploitation attempts, as this vulnerability represents a significant threat to network availability and stability.