CVE-2001-1382 in OpenSSH
Summary
by MITRE
The "echo simulation" traffic analysis countermeasure in OpenSSH before 2.9.9p2 sends an additional echo packet after the password and carriage return is entered, which could allow remote attackers to determine that the countermeasure is being used.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 09/25/2025
The vulnerability described in CVE-2001-1382 pertains to a specific flaw in OpenSSH implementations prior to version 2.9.9p2 where the echo simulation traffic analysis countermeasure exhibits detectable behavior. This countermeasure was designed to obscure the timing patterns that might reveal when a user enters their password, thereby preventing attackers from inferring authentication attempts through timing analysis. The flaw occurs because the system sends an additional echo packet after the password and carriage return are entered, creating a distinguishable pattern that can be detected by remote attackers. This behavior effectively undermines the intended security purpose of the countermeasure by providing observable artifacts that reveal its presence.
The technical implementation of this vulnerability stems from how OpenSSH handled authentication traffic when the echo simulation feature was enabled. When users entered their passwords through SSH connections, the system would normally suppress the echo of characters to prevent timing-based inference of password length and composition. However, the additional echo packet sent after the password submission created a consistent timing pattern that attackers could monitor and analyze. This pattern is particularly problematic because it creates a predictable delay that differs from normal SSH traffic, making it possible for adversaries to determine whether the echo simulation countermeasure was active. The flaw represents a failure in the countermeasure's design where the intended obfuscation mechanism itself becomes a vector for detection.
From an operational impact perspective, this vulnerability significantly weakens the security posture of SSH implementations by allowing attackers to determine when traffic analysis countermeasures are in use. The ability to detect the presence of echo simulation countermeasures provides attackers with valuable intelligence about the target system's security configuration. This detection capability could be leveraged in conjunction with other attack vectors to refine brute force attempts or to focus more sophisticated timing-based attacks. The vulnerability essentially creates a false sense of security for administrators who might believe their systems are protected against timing analysis while simultaneously providing attackers with a clear indicator of the countermeasures in place. This represents a fundamental flaw in the security architecture where defensive mechanisms inadvertently reveal their own existence.
The vulnerability aligns with CWE-209, which addresses information exposure through implementation artifacts, and demonstrates how defensive mechanisms can themselves become security risks when not properly implemented. From an ATT&CK framework perspective, this vulnerability maps to techniques related to reconnaissance and credential access, particularly T1592 for reconnaissance and T1110 for credential access. The detection capability provided by this flaw allows adversaries to tailor their attacks more effectively against SSH services. Organizations should ensure that all SSH implementations are updated to versions that properly handle echo simulation without creating detectable artifacts. The mitigation strategy involves updating to OpenSSH 2.9.9p2 or later versions where the echo simulation mechanism has been corrected to prevent the transmission of additional packets that could be used for detection purposes. Additionally, system administrators should review their SSH configurations to ensure that countermeasures are properly implemented without introducing new vulnerabilities that could be exploited by attackers.