CVE-2001-0155 in VShell
Summary
by MITRE
Format string vulnerability in VShell SSH gateway 1.0.1 and earlier allows remote attackers to execute arbitrary commands via a user name that contains format string specifiers.
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Analysis
by VulDB Data Team • 05/18/2019
The vulnerability identified as CVE-2001-0155 represents a critical format string flaw within VShell SSH gateway version 1.0.1 and earlier implementations. This security weakness stems from improper input validation and handling of user-provided data during string formatting operations. The vulnerability specifically manifests when the SSH gateway processes user authentication requests where the username parameter contains format string specifiers such as %s, %d, or %x. These specifiers are typically used in programming languages like C to define how variables should be formatted when output to console or log files. When an attacker crafts a malicious username containing these format specifiers, the application fails to properly sanitize the input before using it in printf or similar formatting functions.
The technical exploitation of this vulnerability occurs through the manipulation of the format string processing mechanism within the SSH gateway's authentication module. When the system attempts to log or process the malicious username, it interprets the format specifiers as instructions for extracting data from the program's memory stack. This behavior enables attackers to read arbitrary memory locations, potentially exposing sensitive information such as passwords, encryption keys, or system credentials. More critically, skilled attackers can also write data to arbitrary memory locations by carefully crafting the format specifiers, which can lead to arbitrary code execution. The vulnerability operates at the application layer and does not require authentication to exploit, making it particularly dangerous as it can be leveraged by remote attackers without prior access to the system.
The operational impact of CVE-2001-0155 extends beyond simple information disclosure to encompass full system compromise capabilities. An attacker who successfully exploits this vulnerability can execute arbitrary commands on the affected system with the privileges of the SSH gateway process. This access can be leveraged to establish persistent backdoors, escalate privileges, or conduct further reconnaissance within the network environment. The vulnerability affects the core authentication functionality of the SSH gateway, potentially allowing attackers to bypass authentication mechanisms entirely or gain unauthorized access to protected network resources. Organizations using vulnerable versions of VShell SSH gateway face significant risk of unauthorized system access, data breaches, and potential lateral movement within their network infrastructure.
The vulnerability aligns with CWE-134, which specifically addresses the use of format strings inappropriately, and demonstrates characteristics consistent with attack patterns documented in the MITRE ATT&CK framework under the T1078 credential access techniques. Organizations should immediately implement mitigations including upgrading to patched versions of VShell SSH gateway, implementing proper input sanitization for all user-provided data, and deploying network monitoring to detect suspicious authentication patterns. Additionally, system administrators should consider implementing additional security controls such as intrusion detection systems, network segmentation, and regular security audits to reduce the attack surface and detect potential exploitation attempts. The vulnerability also underscores the importance of secure coding practices and input validation, particularly in applications handling user authentication data where improper handling can lead to severe security consequences.