CVE-2026-101995 in Junos OS
Summary
by MITRE • 10/14/2026
An Improper Validation of Specified Quantity in Input vulnerability in the
l2ald
of Juniper Networks Junos OS and Junos OS Evolved allows an adjacent attacker with access to an ICCP peer session to cause memory disclosure and disruption of the l2ald daemon via malformed ICCP packets.
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Analysis
by VulDB Data Team • 10/14/2026
The identified vulnerability represents a critical flaw within the Layer 2 Adjacency Daemon, known as l2ald, in Juniper Networks Junos OS and Junos OS Evolved operating systems. This specific weakness is categorized under CWE-20: Improper Input Validation, specifically relating to the failure to adequately verify the quantity or length of data provided by an external source before processing it. The vulnerability manifests when the system receives Internet Cross Connect Protocol (ICCP) packets that contain malformed headers or payload structures indicating an incorrect specified quantity. Because ICCP is a protocol used for inter-domain communication between provider edge routers, often in service provider environments, the attack surface is limited to adjacent attackers who have established a valid peer session with the affected device. This requirement means the threat actor must already possess network-level access and authentication credentials sufficient to initiate an ICCP connection, which significantly narrows the scope of potential adversaries compared to remote unauthenticated attacks but increases the severity for those within reach.
The technical mechanism behind this flaw involves insufficient bounds checking on input parameters derived from the ICCP packet structure. When a malicious actor sends specially crafted packets with invalid quantity specifications, the l2ald daemon fails to properly validate these values before allocating memory or processing the data structures associated with them. This lack of validation leads to improper handling of buffer sizes, resulting in either out-of-bounds reads that expose sensitive information stored in adjacent memory locations or write operations that corrupt internal state variables. The immediate operational impact is twofold: first, there is a risk of memory disclosure where an attacker may extract proprietary configuration data, routing tables, or other confidential network topology details from the device's memory space. Second, and more critically for availability, the malformed input causes instability within the l2ald process itself, leading to its termination or crash. Since this daemon manages critical Layer 2 adjacency information essential for maintaining connectivity across complex networks, its disruption can result in a denial of service condition affecting adjacent network segments and potentially causing broader outages depending on the redundancy mechanisms in place.
From a strategic security perspective, this vulnerability aligns with ATT&CK technique T1005: Data from Local System, as it facilitates unauthorized access to system memory contents. Furthermore, the disruption caused by the daemon crash falls under T1499: Endpoint Denial of Service or potentially T1213: Data from Information Repositories if the ICCP session is used for exchanging routing policies and topology data. The combination of information disclosure and service disruption makes this a high-severity issue that requires immediate attention in environments where Junos-based infrastructure supports critical inter-domain peering arrangements. Attackers leveraging this flaw can gain deeper visibility into network operations while simultaneously degrading the reliability of core networking functions, creating opportunities for further exploitation or masking other malicious activities during the period of instability.
Mitigation strategies must focus on both technical remediation and operational hardening. The primary defense is to apply the vendor-provided software patches that address the input validation logic within the l2ald component as soon as they become available from Juniper Networks support channels. Until patching can be performed, network segmentation should be strictly enforced to ensure that only trusted, authenticated peers are allowed to establish ICCP sessions with vulnerable devices. Access control lists and firewall rules should restrict source IP addresses for ICCP traffic to known and verified peer routers, thereby preventing unauthorized adjacent hosts from attempting to exploit the flaw. Additionally, enabling logging mechanisms to monitor for unusual patterns in ICCP session establishment or packet sizes can aid in early detection of exploitation attempts. Regular audits of network architecture to minimize unnecessary peering relationships will also reduce the overall attack surface associated with this protocol.