CVE-2000-0993 in FreeBSD
Summary
by MITRE
Format string vulnerability in pw_error function in BSD libutil library allows local users to gain root privileges via a malformed password in commands such as chpass or passwd.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 06/23/2024
The vulnerability described in CVE-2000-0993 represents a critical format string flaw within the BSD libutil library that affects the pw_error function. This vulnerability specifically targets the way password-related commands such as chpass and passwd handle user input during error reporting processes. The flaw occurs when these commands process malformed password inputs and subsequently pass them to the pw_error function without proper sanitization, creating an opportunity for malicious input to be interpreted as format specifiers rather than literal text.
The technical exploitation of this vulnerability relies on the improper handling of user-supplied data within printf-style functions. When the pw_error function receives a malformed password string containing format specifiers such as %s, %d, or %x, these sequences are interpreted by the underlying printf function as instructions for reading from memory locations rather than as literal characters. This misinterpretation allows an attacker to both read arbitrary memory locations and potentially write data to memory addresses, fundamentally compromising the security boundaries of the affected system. The vulnerability operates at the kernel level where privilege escalation occurs, making it particularly dangerous as it can be exploited by local users to gain root privileges without requiring authentication.
From an operational impact perspective, this vulnerability creates a significant risk for systems running BSD-based operating systems that utilize the affected libutil library. The attack vector is straightforward and requires only local access to the system, making it accessible to users with basic account privileges. Once exploited, the vulnerability allows attackers to execute arbitrary code with root privileges, potentially leading to complete system compromise. The exploitation can be achieved through carefully crafted password inputs that contain format string specifiers, enabling the attacker to either dump memory contents for further exploitation or directly manipulate memory to execute malicious code. This vulnerability directly maps to CWE-134 which specifically addresses format string vulnerabilities where format strings are constructed from user-controlled data, and aligns with ATT&CK technique T1068 which involves exploiting vulnerabilities to escalate privileges.
The mitigation strategies for CVE-2000-0993 require immediate system updates and patches from the operating system vendors, as the vulnerability is inherent to the library implementation rather than user configuration. System administrators should ensure that all BSD-based systems have the latest security patches installed, particularly those addressing the libutil library. Additionally, implementing proper input validation and sanitization measures within password handling functions can help prevent malformed input from reaching vulnerable printf-style functions. The recommended approach involves using functions such as snprintf instead of sprintf, and ensuring that all user input passed to formatting functions is properly escaped or validated before processing. Organizations should also consider implementing monitoring solutions to detect unusual patterns in password-related command usage that might indicate exploitation attempts, as this vulnerability represents a classic privilege escalation attack vector that has been widely documented and exploited in various security incidents throughout the early 2000s.