CVE-2004-2069 in OpenSSH
Summary
by MITRE
sshd.c in OpenSSH 3.6.1p2 and 3.7.1p2 and possibly other versions, when using privilege separation, does not properly signal the non-privileged process when a session has been terminated after exceeding the LoginGraceTime setting, which leaves the connection open and allows remote attackers to cause a denial of service (connection consumption).
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Analysis
by VulDB Data Team • 07/06/2025
The vulnerability described in CVE-2004-2069 affects OpenSSH versions 3.6.1p2 and 3.7.1p2, as well as potentially other versions that employ privilege separation mechanisms. This issue specifically targets the sshd.c component within the OpenSSH implementation, which serves as the secure shell daemon responsible for handling incoming SSH connections and managing user authentication processes. The vulnerability arises from improper signaling mechanisms between the privileged and non-privileged processes during session management, creating a critical flaw in the daemon's ability to properly terminate connections when authentication grace periods expire.
The technical flaw manifests when the SSH daemon utilizes privilege separation as a security measure to isolate the privileged components from potentially compromised non-privileged processes. During normal operation, OpenSSH implements a LoginGraceTime setting that defines the maximum time allowed for user authentication before the connection is automatically terminated. When this grace period expires, the privileged sshd process should signal the corresponding non-privileged process to terminate the session and release associated resources. However, in affected versions, this signaling mechanism fails to properly communicate the session termination command, leaving the connection in a stale state where the non-privileged process continues to maintain the connection despite the privileged process having already decided to close it.
This improper signaling creates a resource consumption vulnerability that directly enables denial of service attacks against SSH servers. The connection remains open and active even though the authentication process has been terminated due to exceeding the LoginGraceTime, causing the server to maintain unnecessary connection handles. As attackers can repeatedly establish connections that exceed the grace period, they can accumulate multiple stale connections that consume server resources including memory, file descriptors, and processing power. This resource exhaustion effectively prevents legitimate users from establishing new connections to the SSH service, creating a classic denial of service scenario that impacts system availability.
The vulnerability aligns with CWE-1213, which addresses improper signaling between processes in security-critical applications, and demonstrates a clear failure in proper process communication mechanisms. From an operational perspective, this vulnerability significantly impacts the availability and reliability of SSH services, as it allows remote attackers to consume server resources without requiring authentication or specific privileges. The attack vector is particularly concerning because it can be executed remotely with minimal resources, making it an attractive method for disrupting SSH services in enterprise environments where secure remote access is critical. The issue represents a fundamental flaw in the privilege separation design pattern commonly used in security-critical applications, where proper inter-process communication is essential for maintaining system integrity and resource management.
Mitigation strategies for CVE-2004-2069 primarily involve upgrading to patched versions of OpenSSH that properly implement the signaling mechanism between privileged and non-privileged processes. System administrators should immediately deploy the latest stable OpenSSH releases that contain fixes for this specific vulnerability. Additionally, implementing connection rate limiting and monitoring for unusual connection patterns can help detect and mitigate exploitation attempts. Network-level controls such as firewall rules that limit SSH connection rates from individual sources can provide additional defense in depth. The vulnerability also highlights the importance of proper process communication in security-critical applications and demonstrates how seemingly minor implementation flaws in privilege separation can lead to significant availability impacts. Organizations should conduct regular security assessments of their SSH implementations and ensure proper configuration of LoginGraceTime settings to minimize exposure to this type of resource exhaustion attack. This vulnerability serves as a reminder of the critical importance of proper inter-process communication in security systems and the potential for denial of service impacts from seemingly minor implementation details in privileged code paths.