CVE-2026-101943 in Junos OS
Summary
by MITRE • 10/14/2026
An Improper Input Validation vulnerability in the routing protocol daemon (rpd) of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated network-based attacker to cause a denial of service via a crafted BGP EVPN update message.
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Analysis
by VulDB Data Team • 10/15/2026
The identified vulnerability resides within the Routing Protocol Daemon, commonly referred to as rpd, which is a core component responsible for managing dynamic routing protocols in Juniper Networks Junos OS and Junos OS Evolved environments. This specific flaw constitutes an improper input validation issue that affects the processing of Border Gateway Protocol (BGP) Extended Community Route Type 4 messages, specifically those associated with Ethernet Virtual Private Network (EVPN) updates. The security architecture fails to adequately sanitize or verify the structure and content of incoming BGP EVPN update packets before they are processed by the routing engine. This lack of rigorous validation creates a critical entry point for malicious actors who can exploit this weakness through network-based interactions without requiring any form of authentication, thereby bypassing standard access control mechanisms that might otherwise restrict such operations to authorized peers only.
From an operational perspective, the exploitation of this vulnerability allows an unauthenticated attacker located on the same network segment or reachable via IP connectivity to craft a specially designed BGP EVPN update message. When the vulnerable rpd component processes this malformed packet, it triggers an internal error condition that leads to a crash or hang within the routing process. Since the Routing Protocol Daemon is central to maintaining the forwarding information base and neighbor relationships in Juniper devices, its failure results in a complete denial of service for all BGP sessions managed by that instance. This effectively disrupts network connectivity, causing traffic blackholing, loss of route advertisements, and potential instability across the entire routing domain dependent on this device as an intermediate or edge node. The impact is severe because it compromises the availability pillar of the CIA triad without requiring prior compromise of system credentials or physical access to the hardware.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-20, which describes Improper Input Validation, where software fails to verify that input data meets expected criteria before processing. Furthermore, in the context of the MITRE ATT&CK framework, this exploit technique maps to T1498 Network Denial of Service, specifically under the sub-technique of Direct Network Floods or Protocol-based attacks, as it leverages a specific protocol implementation flaw rather than simple volumetric flooding. The attack vector is classified as network-based and remote, meaning an attacker can execute this from any location where they have IP connectivity to the target device's management or data plane interfaces that accept BGP peering sessions.
Mitigation strategies must focus on both immediate remediation and long-term architectural hardening. The primary defense involves applying the vendor-provided software patches released by Juniper Networks for affected versions of Junos OS and Junos OS Evolved, which address the input validation logic within the rpd component to properly reject malformed EVPN update messages. In environments where patching is not immediately feasible due to operational constraints or testing requirements, network-level controls should be implemented to restrict BGP peering sessions exclusively to known and trusted IP addresses using access control lists or prefix filters. Additionally, enabling strict routing policy validation features available in newer Junos releases can help detect and drop anomalous route advertisements before they reach the vulnerable processing logic. Regular monitoring of BGP session states and logging for unexpected peer resets should also be established to facilitate rapid detection of potential exploitation attempts while mitigation measures are deployed.