CVE-2023-44186 in Junos OS
Summary
by MITRE • 10/25/2023
An Improper Handling of Exceptional Conditions vulnerability in AS PATH processing of Juniper Networks Junos OS and Junos OS Evolved allows an attacker to send a BGP update message with an AS PATH containing a large number of 4-byte ASes, leading to a Denial of Service (DoS). Continued receipt and processing of these BGP updates will create a sustained Denial of Service (DoS) condition.
This issue is hit when the router has Non-Stop Routing (NSR) enabled, has a non-4-byte-AS capable BGP neighbor, receives a BGP update message with a prefix that includes a long AS PATH containing large number of 4-byte ASes, and has to advertise the prefix towards the non-4-byte-AS capable BGP neighbor.
This issue affects:
Juniper Networks Junos OS:
* All versions prior to 20.4R3-S8; * 21.1 versions 21.1R1 and later; * 21.2 versions prior to 21.2R3-S6; * 21.3 versions prior to 21.3R3-S5; * 21.4 versions prior to 21.4R3-S5; * 22.1 versions prior to 22.1R3-S4; * 22.2 versions prior to 22.2R3-S2; * 22.3 versions prior to 22.3R2-S2, 22.3R3-S1; * 22.4 versions prior to 22.4R2-S1, 22.4R3; * 23.2 versions prior to 23.2R2.
Juniper Networks Junos OS Evolved
* All versions prior to 20.4R3-S8-EVO; * 21.1 versions 21.1R1-EVO and later; * 21.2 versions prior to 21.2R3-S6-EVO; * 21.3 versions prior to 21.3R3-S5-EVO; * 21.4 versions prior to 21.4R3-S5-EVO; * 22.1 versions prior to 22.1R3-S4-EVO; * 22.2 versions prior to 22.2R3-S2-EVO; * 22.3 versions prior to 22.3R2-S2-EVO, 22.3R3-S1-EVO; * 22.4 versions prior to 22.4R2-S1-EVO, 22.4R3-EVO; * 23.2 versions prior to 23.2R2-EVO.
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Analysis
by VulDB Data Team • 10/25/2023
This vulnerability represents a critical weakness in the Border Gateway Protocol implementation of Juniper Networks Junos OS and Junos OS Evolved systems, specifically within the AS PATH processing mechanism. The flaw manifests when the system encounters BGP update messages containing exceptionally long AS PATH attributes with numerous 4-byte autonomous system identifiers. This improper handling of exceptional conditions creates a scenario where legitimate network traffic processing becomes overwhelmed, leading to system resource exhaustion and ultimately resulting in a denial of service condition that can persist indefinitely. The vulnerability is particularly concerning because it leverages the standard BGP communication protocol, making it difficult to distinguish malicious traffic from legitimate network operations.
The technical root cause of this vulnerability lies in how the routing system processes AS PATH information when transitioning between different AS number formats. When Non-Stop Routing functionality is enabled, the system must maintain routing state and perform complex transformations when forwarding routes to neighbors that do not support 4-byte AS numbers. This process becomes computationally intensive when processing BGP updates with extended AS PATH sequences, as the system must repeatedly convert and validate these extended path attributes. The flaw occurs during the route advertisement process where the system fails to properly handle the exceptional condition of oversized AS PATH data structures, leading to resource exhaustion rather than graceful error handling or rate limiting mechanisms.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network stability and availability across affected deployments. Networks relying on Juniper routers with NSR enabled and connected to legacy BGP peers that cannot handle 4-byte AS numbers become particularly vulnerable. Attackers can exploit this weakness by crafting BGP update messages with artificially extended AS PATH attributes, causing sustained resource exhaustion that can persist until the affected router is manually restarted or the system is upgraded. This vulnerability affects a broad range of Juniper OS versions, creating widespread exposure across enterprise and service provider networks that depend on these routing platforms for critical infrastructure connectivity.
The vulnerability maps directly to CWE-704 in the Common Weakness Enumeration catalog, which specifically addresses improper handling of exceptional conditions in software systems. This weakness class encompasses scenarios where systems fail to properly manage abnormal or exceptional program states, leading to resource exhaustion or system instability. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1499.004, which involves network disruption through resource exhaustion attacks. The attack surface is particularly broad as it affects both traditional Junos OS and the newer Junos OS Evolved platform, requiring administrators to implement mitigation strategies across multiple product lines and version ranges. Organizations should prioritize immediate patching of affected systems while implementing temporary network segmentation measures to limit exposure during upgrade cycles.
Mitigation strategies should focus on both immediate defensive measures and long-term architectural improvements. Network administrators should prioritize upgrading affected systems to patched versions, with particular attention to the specific version ranges mentioned in the vulnerability advisory. Temporary workarounds include implementing BGP update rate limiting, disabling NSR functionality on affected routers, or filtering BGP updates containing suspiciously long AS PATH attributes. The implementation of proper input validation and resource limits for BGP processing should be considered as part of broader network security hardening efforts. Organizations should also monitor their BGP peer relationships to identify and isolate potentially malicious neighbors that might be exploiting this vulnerability, while maintaining detailed logging of BGP update processing to detect anomalous behavior patterns that could indicate exploitation attempts.