CVE-2015-7750 in Netscreen
Summary
by MITRE
The L2TP packet processing functionality in Juniper Netscreen and ScreenOS Firewall products with ScreenOS before 6.3.0r13-dnd1, 6.3.0r14 through 6.3.0r18 before 6.3.0r18-dnc1, and 6.3.0r19 allows remote attackers to cause a denial of service via a crafted L2TP packet.
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Analysis
by VulDB Data Team • 06/22/2022
The vulnerability identified as CVE-2015-7750 represents a critical denial of service flaw within Juniper Networks ScreenOS firewall implementations that affects multiple software versions including those prior to 6.3.0r13-dnd1 and specific ranges between 6.3.0r14 and 6.3.0r18 before 6.3.0r18-dnc1, as well as 6.3.0r19. This vulnerability specifically targets the Layer 2 Tunneling Protocol packet processing functionality which is essential for establishing secure network connections through virtual private networks. The flaw allows remote attackers to exploit the system by sending specially crafted L2TP packets that trigger unexpected behavior in the firewall's processing mechanisms.
The technical nature of this vulnerability stems from insufficient input validation within the L2TP packet handling code within ScreenOS. When the firewall receives malformed or crafted L2TP packets, the processing logic fails to properly handle these inputs, leading to system instability and eventual denial of service conditions. This represents a classic buffer over-read or improper state handling issue where the system attempts to process data that exceeds expected boundaries or contains unexpected values. The vulnerability manifests as a failure in the packet processing pipeline that causes the firewall to either crash or become unresponsive, effectively preventing legitimate network traffic from being processed through the device.
From an operational impact perspective, this vulnerability poses significant risks to organizations relying on Juniper firewalls for network security. The remote nature of the attack means that adversaries can exploit this flaw from outside the network perimeter without requiring authentication or physical access to the device. Once successfully exploited, the denial of service condition can disrupt network connectivity and compromise the availability of critical services that depend on the firewall for secure communications. The impact extends beyond simple network interruption as organizations may experience extended downtime while administrators work to restore service and implement mitigations, potentially affecting business operations and customer access to network resources.
Security professionals should consider this vulnerability in the context of the ATT&CK framework where it maps to the T1499.004 technique for network denial of service attacks. Organizations should prioritize immediate remediation by upgrading to ScreenOS versions that contain the patched L2TP packet processing functionality, specifically targeting versions that have been released after the identified vulnerable ranges. The mitigation strategy should also include implementing network segmentation and monitoring to detect unusual L2TP traffic patterns that might indicate exploitation attempts. Additionally, organizations should maintain updated threat intelligence feeds and consider deploying intrusion detection systems that can identify and block malformed L2TP packets before they reach the vulnerable firewall components. This vulnerability highlights the importance of proper input validation and robust error handling in network security devices, as outlined in CWE categories related to improper input validation and resource management issues.