CVE-2026-101964 in Junos OS
Summary
by MITRE • 10/15/2026
A Reachable Assertion vulnerability in the routing protocol daemon (rpd) of Juniper Networks Junos OS and Junos OS Evolved allows an adjacent attacker to cause an rpd crash via a crafted LDP packet received over an established LDP session.
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Analysis
by VulDB Data Team • 10/15/2026
The identified security flaw represents a critical integrity violation within the Label Distribution Protocol daemon, commonly referred to as rpd, which is a core component of Juniper Networks' Junos OS and Junos OS Evolved operating systems. This vulnerability manifests specifically as a reachable assertion failure, indicating that the software logic encounters an unexpected state during normal processing operations rather than failing due to memory corruption or buffer overflow in the traditional sense. The root cause lies within the parsing and validation mechanisms of the Label Distribution Protocol handler, where specific input conditions trigger internal consistency checks that are designed to catch programming errors but instead result in a process termination when those expectations are not met by valid yet malformed protocol messages.
An attacker positioned as an adjacent network peer can exploit this weakness by establishing a legitimate LDP session with the vulnerable device and subsequently transmitting specially crafted packets containing specific field values or structural anomalies within the Label Distribution Protocol headers. Because LDP sessions require mutual authentication and state synchronization, the attack does not necessarily require bypassing access controls if the attacker is already authorized to form an adjacency, such as through static neighbor configuration or dynamic discovery mechanisms that do not enforce strict payload validation before assertion checks occur. The crafted packet exploits a logic error where the daemon fails to properly sanitize or validate certain protocol elements prior to executing internal assertions meant for debugging or state verification purposes.
The operational impact of this vulnerability is severe due to its direct effect on service availability and system stability. When the rpd process crashes, it triggers an automatic restart mechanism within Junos OS; however, during the interval between the crash and the daemon's recovery, routing table updates cease, label switching paths are disrupted, and network connectivity may be partially or fully lost depending on the redundancy configuration of the environment. In high-availability deployments where multiple nodes rely on synchronized state information provided by rpd, this disruption can lead to transient black holes in traffic flow, increased latency due to route recalculation upon restart, or potential cascading failures if other control plane processes depend heavily on uninterrupted LDP signaling for MPLS tunnel establishment and maintenance.
From a classification perspective, this vulnerability aligns with CWE-617, which describes Reachable Assertion, as the flaw involves triggering an assertion that should theoretically be unreachable under normal operational conditions but is reachable through malicious input manipulation. Furthermore, in terms of tactical execution within the MITRE ATT&CK framework, this exploit falls under Tactic TA0002 Execution and Technique T1496 Network Service Scanning or potentially T1537 Transfer Data to Cloud Account if viewed broadly as disrupting network services, though more accurately it represents a Denial of Service vector via protocol exploitation. The attack requires low complexity in terms of preparation since the attacker only needs an established LDP session and knowledge of specific packet structures that trigger the assertion failure, making it a viable threat for insider threats or compromised adjacent hosts seeking to degrade network reliability without necessarily gaining persistent access.
Mitigation strategies must focus on both immediate operational controls and long-term architectural improvements. Administrators should prioritize applying vendor-provided software patches as soon as they become available, as these updates typically include code changes that replace the vulnerable assertion with robust input validation logic or remove the unnecessary check entirely if it is redundant. In environments where patching cannot be immediately implemented due to change management cycles or operational constraints, network segmentation policies can be employed to restrict LDP adjacency formation only to trusted and verified peers using access control lists on router interfaces. Additionally, enabling logging for rpd crashes allows security teams to detect attempted exploitation in real time, facilitating rapid incident response while the vulnerability remains unpatched. Regular review of routing protocol configurations ensures that unnecessary adjacencies are removed, thereby reducing the attack surface available to potential adversaries seeking to trigger this assertion failure and disrupt critical network infrastructure services.