CVE-2024-39555 in Junos OS
Summary
by MITRE • 07/11/2024
An Improper Handling of Exceptional Conditions vulnerability in the Routing Protocol Daemon (RPD) of Juniper Networks Junos OS and Junos OS Evolved allows an attacker sending a specific malformed BGP update message to cause the session to reset, resulting in a Denial of Service (DoS). Continued receipt and processing of these malformed BGP update messages will create a sustained Denial of Service (DoS) condition.
Upon receipt of a BGP update message over an established BGP session containing a specifically malformed tunnel encapsulation attribute, when segment routing is enabled, internal processing of the malformed attributes within the update results in improper parsing of remaining attributes, leading to session reset:
BGP SEND Notification code 3 (Update Message Error) subcode 1 (invalid attribute list)
Only systems with segment routing enabled are vulnerable to this issue.
This issue affects eBGP and iBGP, in both IPv4 and IPv6 implementations, and requires a remote attacker to have at least one established BGP session.
This issue affects:
Junos OS:
* All versions before 21.4R3-S8, * from 22.2 before 22.2R3-S4, * from 22.3 before 22.3R3-S3, * from 22.4 before 22.4R3-S3, * from 23.2 before 23.2R2-S1, * from 23.4 before 23.4R1-S2, 23.4R2.
Junos OS Evolved:
* All versions before 21.4R3-S8-EVO, * from 22.2-EVO before 22.2R3-S4-EVO, * from 22.3-EVO before 22.3R3-S3-EVO, * from 22.4-EVO before 22.4R3-S3-EVO, * from 23.2-EVO before 23.2R2-S1-EVO, * from 23.4-EVO before 23.4R1-S2-EVO, 23.4R2-EVO.
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Analysis
by VulDB Data Team • 04/29/2026
The vulnerability described in CVE-2024-39555 represents a critical improper handling of exceptional conditions within the Routing Protocol Daemon (RPD) of Juniper Networks Junos OS and Junos OS Evolved systems. This flaw manifests when the RPD processes malformed BGP update messages containing specifically crafted tunnel encapsulation attributes while segment routing is enabled. The issue stems from inadequate error handling during attribute parsing, which leads to unexpected behavior in the BGP session management process. According to the Common Weakness Enumeration standard CWE-391, this vulnerability aligns with improper handling of exceptional conditions, where the system fails to properly manage error states during data processing. The vulnerability specifically targets the internal processing logic of BGP updates, where the malformed tunnel encapsulation attribute triggers a cascading parsing failure that affects subsequent attributes within the same update message.
The technical impact of this vulnerability extends beyond simple session disruption to create sustained denial of service conditions that can severely impact network operations. When a remote attacker sends a malformed BGP update message containing the specific tunnel encapsulation attribute, the system's internal processing logic fails to handle the exceptional condition gracefully. Instead of gracefully rejecting the malformed data and maintaining session stability, the system resets the BGP session, generating a BGP SEND Notification with code 3 (Update Message Error) and subcode 1 (invalid attribute list). This behavior creates a DoS condition that can be perpetuated through continued receipt of malformed messages, effectively preventing legitimate routing updates from being processed and disrupting network connectivity. The vulnerability's impact is particularly severe because it affects both eBGP and iBGP implementations across both IPv4 and IPv6 protocols, providing attackers with multiple attack vectors.
The operational implications of CVE-2024-39555 are significant for network infrastructure relying on Juniper devices with segment routing enabled. The vulnerability requires only a single established BGP session to exploit, making it particularly dangerous in production environments where BGP sessions are continuously active. Network administrators face the challenge of maintaining routing stability while dealing with potential DoS attacks that can be executed from remote locations with minimal privileges required. The attack vector follows the ATT&CK framework's T1499.004 technique for network denial of service, where adversaries leverage protocol implementation weaknesses to disrupt service availability. Systems that have segment routing enabled become particularly vulnerable because this feature introduces additional processing paths that can be exploited through the malformed attribute handling. The sustained DoS condition created by this vulnerability can lead to cascading failures throughout the network infrastructure, as routing disruptions affect the connectivity of multiple network segments and potentially cause service outages.
Mitigation strategies for CVE-2024-39555 focus primarily on implementing software updates and operational controls to prevent exploitation. Organizations should immediately upgrade their Junos OS and Junos OS Evolved systems to versions that contain the patched RPD handling logic for malformed BGP attributes. The affected versions span multiple release branches, requiring careful assessment and deployment planning to ensure complete protection across the network infrastructure. Network operators should also consider implementing BGP session filtering and rate limiting mechanisms as defensive measures to reduce the impact of potential attacks. Additionally, monitoring systems should be configured to detect unusual BGP update patterns and notification messages that could indicate exploitation attempts. The vulnerability's specific requirement for segment routing to be enabled means that network administrators can also consider temporarily disabling this feature as a temporary mitigation while planning full patches. According to industry best practices for vulnerability management, organizations should conduct thorough testing of patches in non-production environments before deployment to ensure compatibility with existing network configurations and prevent unintended service disruptions.