CVE-2020-1639 in Junos
Summary
by MITRE
When an attacker sends a specific crafted Ethernet Operation, Administration, and Maintenance (Ethernet OAM) packet to a target device, it may improperly handle the incoming malformed data and fail to sanitize this incoming data resulting in an overflow condition. This overflow condition in Juniper Networks Junos OS allows an attacker to cause a Denial of Service (DoS) condition by coring the CFM daemon. Continued receipt of these packets may cause an extended Denial of Service condition. This issue affects: Juniper Networks Junos OS 12.3 versions prior to 12.3R12-S15; 12.3X48 versions prior to 12.3X48-D95 on SRX Series; 14.1X50 versions prior to 14.1X50-D145; 14.1X53 versions prior to 14.1X53-D47; 15.1 versions prior to 15.1R2; 15.1X49 versions prior to 15.1X49-D170 on SRX Series; 15.1X53 versions prior to 15.1X53-D67.
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Analysis
by VulDB Data Team • 05/17/2024
The vulnerability described in CVE-2020-1639 represents a critical buffer overflow condition within the Ethernet Operations, Administration, and Maintenance (OAM) implementation of Juniper Networks Junos OS. This flaw specifically manifests when the target device receives crafted Ethernet OAM packets that contain malformed data structures. The issue stems from insufficient input validation and sanitization mechanisms within the CFM (Connectivity Fault Management) daemon, which is responsible for monitoring network connectivity and fault detection in Ethernet networks. The vulnerability affects multiple versions of Junos OS across different product lines including SRX Series firewalls, making it particularly concerning for network infrastructure deployments that rely on these devices for security and connectivity management.
The technical exploitation of this vulnerability occurs through the improper handling of Ethernet OAM packets that contain oversized or malformed data fields. When the CFM daemon processes these crafted packets, it fails to properly validate the incoming data length and structure, leading to a buffer overflow condition in memory management. This overflow causes the daemon to crash and core dump, resulting in an immediate denial of service condition that affects the device's ability to perform connectivity monitoring and fault detection functions. The vulnerability is particularly dangerous because it requires minimal network access for exploitation, as attackers only need to send specific Ethernet OAM packets to the target device to trigger the condition. According to CWE classification, this represents a buffer overflow vulnerability categorized under CWE-121, which specifically addresses stack-based buffer overflow conditions that occur when insufficient bounds checking is performed.
The operational impact of CVE-2020-1639 extends beyond simple service disruption, as the continued receipt of malicious packets can maintain extended denial of service conditions that may persist until the device is manually restarted or the vulnerable software is patched. Network administrators face significant challenges in detecting and mitigating this vulnerability since the malicious packets appear as legitimate network traffic and can be difficult to distinguish from normal OAM communications. The affected versions span multiple Junos OS releases, indicating that this vulnerability has been present for an extended period and affects a substantial portion of deployed network infrastructure. Organizations using SRX Series devices are particularly at risk given the widespread deployment of these security appliances in enterprise and service provider networks where continuous connectivity monitoring is critical for network operations and security enforcement.
Mitigation strategies for this vulnerability require immediate implementation of software patches provided by Juniper Networks, as the company has released specific versions that address the buffer overflow condition in the CFM daemon. Network administrators should prioritize patching affected devices according to Juniper's security advisory, focusing on the specific version ranges mentioned in the CVE description. Additionally, network segmentation and access control measures can help limit the attack surface by restricting network access to devices running vulnerable versions of Junos OS. Implementing network monitoring solutions that can detect anomalous OAM packet patterns may also provide early warning capabilities, though this approach has limitations given that the malicious packets appear legitimate. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving privilege escalation and denial of service through protocol manipulation, specifically targeting network infrastructure components that are essential for maintaining network connectivity and security operations.