CVE-2000-0994 in OpenBSD
Summary
by MITRE
Format string vulnerability in OpenBSD fstat program (and possibly other BSD-based operating systems) allows local users to gain root privileges via the PWD environmental variable.
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Analysis
by VulDB Data Team • 01/06/2025
The vulnerability described in CVE-2000-0994 represents a critical format string flaw within the OpenBSD fstat program that demonstrates the dangerous implications of improper input validation in system utilities. This vulnerability specifically targets the handling of the PWD environment variable, which is commonly used to track the current working directory in Unix-like systems. The flaw occurs when the fstat program processes user-supplied data without proper sanitization, creating an opportunity for malicious input to be interpreted as format specifiers rather than literal values. This type of vulnerability falls under the CWE-134 category of Use of Externally-Controlled Format String, which is classified as a high-severity weakness due to its potential for arbitrary code execution and privilege escalation.
The technical exploitation of this vulnerability requires a local attacker to manipulate the PWD environment variable in a specific manner that triggers the format string parsing error within the fstat program. When the program attempts to format and display information using the untrusted PWD value, the attacker can inject format specifiers that allow them to read from or write to memory locations. This memory corruption can be leveraged to overwrite critical program variables or function pointers, ultimately enabling the execution of arbitrary code with the privileges of the target process. The vulnerability is particularly concerning because it operates at the local level, meaning that an attacker who already has access to a user account can escalate their privileges to root, bypassing normal security boundaries that protect system integrity.
The operational impact of CVE-2000-0994 extends beyond simple privilege escalation as it represents a fundamental flaw in how system utilities handle environment variables and user input. This vulnerability affects not only OpenBSD systems but potentially other BSD-based operating systems that implement similar fstat functionality, making it a widespread concern for organizations running these platforms. The attack vector is relatively simple to execute, requiring only the manipulation of environment variables and the execution of the vulnerable program, which means that even less sophisticated attackers could potentially exploit this weakness. This vulnerability aligns with the ATT&CK technique T1068 for Local Privilege Escalation and demonstrates how seemingly innocuous system utilities can serve as attack vectors for more serious security breaches.
Mitigation strategies for this vulnerability require immediate patching of affected systems, as the fix typically involves implementing proper input validation and sanitization within the fstat program. Organizations should ensure that all environment variables are properly escaped or validated before being used in format string operations, and that system utilities do not directly incorporate user-supplied data into their output formatting without appropriate safeguards. The vulnerability also highlights the importance of secure coding practices and the need for regular security auditing of system utilities, particularly those that run with elevated privileges. Additionally, system administrators should consider implementing runtime protections such as stack canaries and address space layout randomization to make exploitation more difficult even if the underlying vulnerability remains unpatched. The remediation process should include comprehensive testing to ensure that the patch does not introduce regressions in system functionality while effectively addressing the format string vulnerability.