CVE-2026-102033 in Junos OS
Summary
by MITRE • 10/14/2026
An Improper Validation of Specified Quantity in Input vulnerability in l2ald of Juniper Networks Junos OS and Junos OS Evolved allows an adjacent attacker to cause a denial of service via an ICCP MC-LAG message.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/14/2026
The identified vulnerability represents a critical flaw within the Layer 2 Advanced (l2ald) component of Juniper Networks Junos Operating System and Junos OS Evolved, specifically affecting devices configured for Multi-Chassis Link Aggregation Group (MC-LAG) deployments using the Inter-Cluster Communication Protocol (ICCP). This security issue is classified as an Improper Validation of Specified Quantity in Input, which aligns with CWE-20: Improper Input Validation. The core technical deficiency lies in the application's failure to adequately verify or bound specific numerical values contained within incoming ICCP messages before processing them. When a device receives these control plane packets from an adjacent peer in an MC-LAG setup, it expects certain parameters to fall within predefined operational limits. However, due to this validation gap, maliciously crafted inputs containing excessively large or malformed quantity specifications can bypass internal checks and trigger unhandled exceptions or resource exhaustion conditions during parsing routines.
From a technical perspective, the vulnerability exploits the trust relationship inherent in ICCP communications between chassis members of an MC-LAG cluster. In such architectures, devices exchange state information to maintain consistency across the multi-chassis link aggregation group. The attacker, positioned as an adjacent node on the network segment connected via ICCP links, can craft specific packets that exploit this lack of rigorous input sanitization. By injecting messages with invalid quantity fields, the attacker forces the l2ald process into a failure state. This typically manifests as a segmentation fault or a crash in the control plane daemon responsible for managing Layer 2 forwarding decisions and cluster synchronization. The absence of robust boundary checks allows these malformed packets to consume excessive memory or CPU resources during validation attempts, leading directly to service disruption.
The operational impact of this vulnerability is severe, primarily resulting in a Denial of Service (DoS) condition against the affected Juniper device. Since l2ald plays a pivotal role in maintaining cluster integrity and forwarding state for MC-LAG configurations, its compromise can lead to instability across the entire network segment dependent on that chassis. An adjacent attacker who successfully exploits this flaw can cause the control plane process to restart or crash entirely. In high-availability environments, such crashes may trigger failover events, causing temporary loss of connectivity for end users and potential data packet loss during the re-synchronization phase. Furthermore, repeated exploitation attempts could lead to persistent instability, requiring manual intervention by network administrators to restore normal operations through device reboots or process restarts, thereby impacting business continuity and operational efficiency.
This vulnerability is categorized under MITRE ATT&CK technique T1499: Endpoint Denial of Service, as it involves the deliberate exhaustion or disruption of system resources leading to service unavailability. It also relates to CWE-787: Out-of-bounds Write if the improper validation leads to memory corruption, although the primary reported impact is denial of service through process instability. To mitigate this risk, organizations must ensure that all Juniper Networks devices running affected versions of Junos OS and Junos OS Evolved are updated to the latest software releases provided by Juniper Networks, which contain patches for this specific input validation flaw. Additionally, network segmentation strategies should be employed to restrict ICCP traffic only between authorized peer nodes, preventing unauthorized adjacent hosts from attempting to send crafted packets. Implementing strict access control lists on interfaces carrying ICCP traffic and monitoring for anomalous control plane packet rates can further reduce the attack surface and provide early detection of exploitation attempts.