CVE-2008-0852 in FreeSSHD
Summary
by MITRE
freeSSHd 1.2 and earlier allows remote attackers to cause a denial of service (crash) via a SSH2_MSG_NEWKEYS packet to TCP port 22, which triggers a NULL pointer dereference.
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Analysis
by VulDB Data Team • 12/21/2024
The vulnerability identified as CVE-2008-0852 affects freeSSHd version 1.2 and earlier, presenting a critical security flaw that enables remote attackers to execute a denial of service attack against SSH servers. This vulnerability specifically targets the SSH2_MSG_NEWKEYS packet implementation within the SSH protocol stack, making it particularly dangerous as it exploits a fundamental aspect of secure remote access communications. The flaw manifests when the server receives a malformed SSH2_MSG_NEWKEYS packet on the standard SSH port 22, causing the application to crash and become unavailable to legitimate users. This type of vulnerability represents a classic null pointer dereference issue, where the software fails to properly validate incoming packet data before attempting to access memory locations, leading to an immediate application termination.
The technical implementation of this vulnerability stems from inadequate input validation within the SSH protocol handler of freeSSHd. When processing the SSH2_MSG_NEWKEYS packet, the software does not properly verify the integrity or structure of the incoming data before attempting to dereference pointers that may be null or improperly initialized. This particular flaw aligns with CWE-476, which describes null pointer dereference conditions that can lead to application crashes and system instability. The attack vector requires minimal privileges as it operates over the network, allowing any remote attacker to send specially crafted packets to the target system without authentication. The vulnerability exists at the protocol parsing layer, making it particularly effective as it targets the core functionality of the SSH service rather than application-specific features.
From an operational perspective, this vulnerability presents significant risk to organizations relying on freeSSHd for remote access management. The denial of service impact means that legitimate users cannot establish secure connections to affected systems, potentially disrupting business operations and creating security gaps where unauthorized access might be attempted during service outages. The crash occurs immediately upon packet reception, providing no opportunity for graceful error handling or logging, which makes detection and forensic analysis more challenging. This vulnerability directly impacts the availability aspect of the CIA triad, compromising the system's ability to provide continuous service. The attack can be executed repeatedly, allowing for sustained denial of service conditions that could be used as part of larger attack campaigns or as a distraction during other malicious activities.
The mitigation strategies for this vulnerability require immediate action from affected organizations, including upgrading to freeSSHd version 1.3 or later where the issue has been resolved through proper input validation and null pointer checks. Network administrators should implement firewall rules to restrict access to port 22 from trusted networks only, while also monitoring for suspicious SSH traffic patterns. The remediation process should include thorough testing of updated software in controlled environments before deployment to production systems. Organizations should also consider implementing intrusion detection systems that can identify and alert on malformed SSH packets that match the vulnerability signature. From an ATT&CK framework perspective, this vulnerability aligns with techniques related to service stoppage and availability denial, specifically targeting the system's ability to maintain operational continuity. The vulnerability demonstrates how protocol-level flaws can be exploited to create cascading effects that compromise not just individual systems but entire network infrastructures.