CVE-2002-0083 in OpenSSH
Summary
by MITRE
Off-by-one error in the channel code of OpenSSH 2.0 through 3.0.2 allows local users or remote malicious servers to gain privileges.
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Analysis
by VulDB Data Team • 09/23/2025
The vulnerability described in CVE-2002-0083 represents a critical off-by-one error within the channel handling code of OpenSSH versions 2.0 through 3.0.2, creating a security flaw that can be exploited by both local users and remote malicious servers to escalate privileges. This type of error occurs when a program manipulates array indices or buffer boundaries incorrectly, leading to memory corruption that can be leveraged for privilege escalation. The flaw specifically resides in how OpenSSH processes channel-related operations, making it particularly dangerous as channel code typically handles sensitive operations within the SSH protocol implementation. Such vulnerabilities fall under CWE-129, which addresses improper validation of array indices, and represent a fundamental weakness in input boundary checking that can lead to memory corruption and privilege escalation.
The technical implementation of this vulnerability exploits the improper handling of channel data structures during SSH session establishment and communication. When OpenSSH processes channel requests, the off-by-one error occurs in the boundary checking logic that determines valid channel identifiers or buffer sizes. This flaw allows an attacker to manipulate channel parameters in such a way that they can overwrite adjacent memory locations, potentially corrupting critical data structures or executing arbitrary code with elevated privileges. The vulnerability affects both local privilege escalation scenarios where a user can exploit the flaw locally and remote exploitation scenarios where malicious SSH servers can target connected clients. The impact extends beyond simple privilege escalation as it can potentially allow attackers to bypass authentication mechanisms or execute arbitrary commands on the target system.
The operational impact of CVE-2002-0083 is severe and multifaceted, particularly given that OpenSSH was widely deployed as the standard secure shell implementation across Unix and Linux systems. Systems running vulnerable versions of OpenSSH were at risk of complete compromise when users connected to untrusted SSH servers or when local users could manipulate channel-related operations. The vulnerability's exploitation potential spans multiple attack vectors, including man-in-the-middle attacks where malicious servers can exploit client vulnerabilities, and local privilege escalation where attackers can leverage the flaw to gain root access. This type of vulnerability aligns with ATT&CK technique T1068, which covers local privilege escalation through exploitation of system vulnerabilities, and T1566, which covers phishing attacks that can be used to deliver malicious SSH servers. The widespread deployment of affected OpenSSH versions meant that many systems across different environments were potentially vulnerable to this flaw.
Mitigation of CVE-2002-0083 requires immediate patching of affected OpenSSH installations to versions that address the channel boundary checking error. System administrators should upgrade to OpenSSH 3.1 or later, which contains the necessary fixes for this vulnerability. In addition to patching, organizations should implement network segmentation and monitoring to detect potential exploitation attempts, particularly in environments where untrusted SSH servers might be accessed. The vulnerability highlights the importance of proper input validation and boundary checking in security-critical code, aligning with security best practices outlined in the CERT/CC secure coding guidelines and OWASP secure coding practices. Organizations should also consider implementing SSH key management policies and monitoring for unusual channel activity that might indicate exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify other potential vulnerabilities in SSH implementations and ensure comprehensive protection against similar flaws in the future.