CVE-2026-101962 in Junos OS
Summary
by MITRE • 10/15/2026
An Improper Handling of Length Parameter Inconsistency vulnerability in the routing protocol daemon (rpd) of Juniper Networks Junos OS and Junos OS Evolved allows an attacker sending a specifically malformed BGP EVPN multicast update which is attempted to be readvertised to cause an rpd crash.
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Analysis
by VulDB Data Team • 10/15/2026
The identified vulnerability resides within the routing protocol daemon, known as rpd, of Juniper Networks Junos Operating System and Junos OS Evolved platforms. This component serves as the central engine for managing dynamic routing protocols, including Border Gateway Protocol (BGP), which is critical for exchanging network reachability information between autonomous systems on the internet or within large enterprise networks. The specific flaw involves an improper handling of length parameter inconsistencies when processing BGP Extended Community attributes associated with Ethernet Virtual Private Network (EVPN) multicast updates. EVPN is a standard that enables Layer 2 and Layer 3 virtual private networking over MPLS or IP networks, while multicast functionality allows efficient one-to-many data transmission. The vulnerability manifests specifically during the process where an incoming update is evaluated for potential readvertisement to other peers in the routing table.
The technical root cause of this issue lies in a failure to adequately validate the length fields contained within malformed BGP EVPN multicast updates before they are processed by the rpd logic. When an attacker sends a specially crafted packet containing these inconsistencies, the daemon attempts to parse and subsequently readvertise the update. During this parsing phase, the software fails to correctly interpret or bound-check the length parameters associated with specific attributes in the message header. This discrepancy leads to memory corruption or an out-of-bounds access condition within the rpd process space. Because BGP is a stateful protocol that maintains extensive session and route table information, such internal errors typically result in immediate termination of the daemon process to prevent further system instability.
The operational impact of this vulnerability is severe due to its potential for remote exploitation without authentication. An attacker positioned on the network path between routing peers can trigger a denial-of-service condition by sending the malformed update. The resulting crash of the rpd process causes an interruption in all dynamic routing operations managed by that daemon. This includes the loss of BGP sessions, withdrawal of learned routes, and potential disruption to traffic forwarding decisions across the affected router or switch. In high-availability environments where multiple instances might be running, this could lead to failover events, increased latency, or complete network partitioning depending on the redundancy configuration. The impact is particularly acute in service provider networks or large data centers that rely heavily on EVPN for scalable multi-tenant isolation and efficient multicast distribution.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the system fails to verify that input data conforms to expected structural constraints before processing. It also relates to CWE-134 Use of Externally-Controlled Format String or CWE-787 Out-of-bounds Write depending on the specific memory corruption mechanism triggered by the length inconsistency. In terms of adversary tactics, this aligns with MITRE ATT&CK technique T1499 Endpoint Denial of Service, where an attacker aims to disrupt availability rather than compromise confidentiality or integrity. The attack vector is classified as Network-based and requires no user interaction, making it a high-severity remote vulnerability that demands immediate attention from network security teams.
Mitigation strategies should focus on both preventive controls and operational hardening. Juniper Networks has likely released software updates addressing this specific parsing logic error; therefore, applying the latest recommended version of Junos OS or Junos OS Evolved is the primary remediation step. Until patches are applied, administrators can implement ingress filtering policies to drop BGP packets that contain malformed attributes or unexpected length fields before they reach the routing engine. Access Control Lists (ACLs) should be configured to restrict BGP peering relationships only to trusted and verified IP addresses, thereby limiting the attack surface for external adversaries. Additionally, enabling BGP route dampening and monitoring logs for rpd restart events can help in early detection of exploitation attempts or accidental triggers. Regular auditing of routing configurations and ensuring that network infrastructure is segmented to limit lateral movement are also critical components of a defense-in-depth strategy against such protocol-level vulnerabilities.