CVE-2002-0175 in Libsafe
Summary
by MITRE
libsafe 2.0-11 and earlier allows attackers to bypass protection against format string vulnerabilities via format strings that use the " " and "I" characters, which are implemented in libc but not libsafe.
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Analysis
by VulDB Data Team • 06/17/2024
The vulnerability described in CVE-2002-0175 represents a critical flaw in the libsafe library version 2.0-11 and earlier, which was designed to provide protection against format string vulnerabilities in Unix-like systems. This security weakness specifically targets the implementation of format string checking mechanisms that were intended to prevent malicious exploitation of programs vulnerable to format string attacks. The libsafe library operated as a dynamic library that intercepted potentially dangerous format string operations and analyzed them for suspicious patterns that could indicate an attempt to exploit buffer overflow vulnerabilities.
The technical flaw in libsafe stems from its incomplete implementation of format string validation logic, which fails to account for certain legitimate format specifiers that are part of the standard C library libc. Specifically, the library does not properly recognize or handle format strings that utilize the space character " " and the capital letter "I" as format specifiers, which are valid components of the printf family of functions within libc. This gap in the validation logic creates a bypass condition where attackers can craft format strings that appear benign to libsafe's protection mechanisms while still maintaining the malicious intent to exploit format string vulnerabilities.
The operational impact of this vulnerability extends beyond simple bypass of security protections, as it allows attackers to circumvent automated defenses that were specifically designed to prevent format string attacks. When an application is linked with libsafe and runs with this library active, the protection mechanisms fail to detect or block malicious format strings that contain these specific character sequences. This creates a false sense of security for system administrators who may believe their applications are protected against format string vulnerabilities when in reality they remain exposed to exploitation. The vulnerability particularly affects applications that perform printf-style operations on user-supplied data without proper validation, making it a significant concern for network services and applications handling untrusted input.
This vulnerability aligns with CWE-134, which describes the weakness of using format strings from external sources without proper validation, and represents a classic case of incomplete input validation in security software. The bypass mechanism leverages legitimate library functionality to evade protection, demonstrating how security implementations can be undermined by incomplete understanding of standard library behaviors. From an ATT&CK perspective, this vulnerability maps to technique T1059.007 for Command and Scripting Interpreter: Unix Shell and T1211 for Exploitation for Privilege Escalation, as attackers can leverage the bypass to execute arbitrary code through format string exploitation. The flaw essentially allows adversaries to perform privilege escalation attacks by exploiting format string vulnerabilities that would normally be blocked by libsafe's protection mechanisms, making it a particularly dangerous weakness in system security configurations.
Mitigation strategies for this vulnerability require immediate removal of the vulnerable libsafe library version from affected systems and replacement with more comprehensive protection mechanisms. Organizations should implement proper input validation and sanitization for all printf-style operations, particularly those involving user-supplied data. The recommended approach includes using modern compiler security features such as stack canaries, address space layout randomization, and fortified library functions that provide better protection against format string vulnerabilities. Additionally, system administrators should consider implementing application-level sandboxing and runtime monitoring to detect and prevent exploitation attempts. Regular security audits and vulnerability assessments should be conducted to identify and remediate similar implementation gaps in other security protection mechanisms. The fundamental lesson from this vulnerability is the importance of complete specification compliance and thorough testing of security implementations against all standard library behaviors to prevent such bypass conditions.