CVE-2026-101942 in Junos OS
Summary
by MITRE • 10/15/2026
An Improper Handling of Length Parameter Inconsistency vulnerability in the routing protocol daemon (rpd) process of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated network-based attacker to cause a denial of service via a malformed EVPN Type-3 or Type-4 route received from a configured EVPN peer and processed during re-advertisement.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified as Improper Handling of Length Parameter Inconsistency resides within the routing protocol daemon, known as rpd, which is a core component of Juniper Networks Junos OS and Junos OS Evolved operating systems. This specific flaw affects the processing logic for Ethernet Virtual Private Network (EVPN) routes, particularly Type-3 and Type-4 route advertisements. The root cause lies in how the software validates length parameters associated with these BGP extended community attributes during the re-advertisement process. When a router receives an EVPN update from a configured peer, it parses various fields to determine reachability and path selection criteria. In this instance, the daemon fails to adequately verify that the declared length of certain data structures matches their actual size or expected bounds before proceeding with memory allocation or processing operations. This lack of rigorous input validation creates a scenario where malformed packets can trigger unexpected behavior within the application logic.
An unauthenticated network-based attacker who has reachability to the affected device and is configured as an EVPN peer can exploit this inconsistency by sending specially crafted BGP updates containing Type-3 or Type-4 routes with incorrect length fields. Because the vulnerability occurs during re-advertisement, the attack does not necessarily require immediate processing of the initial route but rather exploits the subsequent step where the router attempts to propagate or manipulate the route information within its local routing table and potentially to other peers. The improper handling leads to a state inconsistency that causes the rpd process to crash or become unresponsive. Since the routing daemon is critical for maintaining network connectivity, its failure results in an immediate denial of service condition. Traffic relying on dynamic routing protocols may be dropped, leading to significant disruption in network operations and potential loss of availability for services dependent on those routes.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, specifically regarding the failure to validate length parameters which can lead to memory corruption or logical errors. It also maps to MITRE ATT&CK technique T1498 Network Denial of Service, as the primary impact is the disruption of service availability rather than unauthorized access or data exfiltration. The attack vector is classified as network-based and requires no prior authentication, making it particularly dangerous in environments where BGP peering relationships are established with external partners or across untrusted segments without sufficient filtering mechanisms.
Mitigation strategies should focus on both immediate remediation and long-term architectural defenses. Juniper Networks has released software updates that patch the validation logic within the rpd process to correctly handle length parameter inconsistencies, preventing the crash condition. Administrators must apply these patches promptly to all affected devices in their infrastructure. In addition to updating software, network operators should implement strict BGP filtering policies using prefix lists and route maps to validate incoming EVPN advertisements from peers. By rejecting malformed or unexpected route attributes before they reach the routing engine, organizations can reduce the attack surface even if a vulnerability exists. Furthermore, enabling logging for BGP session resets and monitoring rpd process stability can help in early detection of such exploitation attempts, allowing for rapid incident response to minimize downtime.