CVE-2002-1547 in Netscreen ScreenOS
Summary
by MITRE
Netscreen running ScreenOS 4.0.0r6 and earlier allows remote attackers to cause a denial of service via a malformed SSH packet to the Secure Command Shell (SCS) management interface, as demonstrated via certain CRC32 exploits, a different vulnerability than CVE-2001-0144.
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Analysis
by VulDB Data Team • 09/04/2025
The vulnerability identified as CVE-2002-1547 affects Netscreen devices running ScreenOS version 4.0.0r6 and earlier, specifically targeting the Secure Command Shell management interface. This flaw represents a critical denial of service condition that can be exploited remotely through the transmission of malformed SSH packets. The vulnerability specifically impacts the SCS management interface, which provides administrators with secure command line access to the device configuration and monitoring capabilities. The attack vector involves sending specially crafted SSH packets that contain malformed CRC32 checksums, which triggers unexpected behavior in the device's processing mechanisms.
The technical implementation of this vulnerability stems from insufficient input validation within the SSH protocol implementation of the ScreenOS operating system. When the device receives a malformed SSH packet containing invalid CRC32 data, the system fails to properly handle the malformed data structure, leading to a complete system crash or restart. This particular weakness falls under CWE-129, which describes improper validation of input boundaries, and more specifically aligns with CWE-20, representing improper input validation. The vulnerability operates at the protocol level within the SSH implementation, where the system does not adequately sanitize or validate the checksum values contained within the SSH packets before processing them.
The operational impact of this vulnerability extends beyond simple service disruption, as it can result in complete device unavailability for administrative access and monitoring purposes. Network administrators who rely on the SCS interface for device management would find their systems inaccessible during an attack, potentially leading to extended downtime for network security operations. The vulnerability demonstrates characteristics consistent with the ATT&CK framework's T1499.004 technique, which involves network denial of service attacks targeting network infrastructure devices. Additionally, the attack can be classified under T1566.001, representing the use of spearphishing with malicious attachments, though in this case the attack vector is through network protocol manipulation rather than email-based delivery.
Mitigation strategies for CVE-2002-1547 require immediate implementation of firmware updates to ScreenOS version 4.0.0r7 or later, which contain patches addressing the malformed SSH packet handling. Network administrators should also implement network segmentation to limit access to the SCS management interface, restricting access to only trusted administrative networks. Additionally, implementing intrusion detection systems that can identify and block malformed SSH packets may provide an additional layer of protection. The vulnerability highlights the importance of proper input validation in network protocol implementations and serves as a reminder of the critical need for regular security updates in network infrastructure devices. Organizations should also consider implementing redundant management access methods and maintaining detailed operational procedures for device recovery in case of denial of service attacks.