CVE-2012-3406 in Ubuntu Linux
Summary
by MITRE
The vfprintf function in stdio-common/vfprintf.c in GNU C Library (aka glibc) 2.5, 2.12, and probably other versions does not "properly restrict the use of" the alloca function when allocating the SPECS array, which allows context-dependent attackers to bypass the FORTIFY_SOURCE format-string protection mechanism and cause a denial of service (crash) or possibly execute arbitrary code via a crafted format string using positional parameters and a large number of format specifiers, a different vulnerability than CVE-2012-3404 and CVE-2012-3405.
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Analysis
by VulDB Data Team • 03/11/2022
The vulnerability described in CVE-2012-3406 represents a critical flaw in the GNU C Library's implementation of the vfprintf function, which serves as a core component in C program execution and string formatting operations. This vulnerability specifically targets the memory allocation mechanism used within the function when processing format strings, creating a potential pathway for attackers to circumvent security protections that are designed to prevent buffer overflows and format string attacks. The flaw affects glibc versions 2.5 and 2.12, though likely extends to other versions in the same family, making it a widespread concern across numerous Linux distributions and Unix-like systems. The vulnerability operates through a sophisticated manipulation of the stack allocation process that undermines the intended security measures.
The technical mechanism behind this vulnerability involves the improper restriction of the alloca function usage within the SPECS array allocation process during format string processing. The alloca function dynamically allocates memory on the stack, and when this allocation is not properly bounded or restricted, it creates opportunities for attackers to manipulate the stack layout. In this specific case, context-dependent attackers can craft format strings that utilize positional parameters combined with a large number of format specifiers to trigger the flawed memory allocation behavior. This allows the attacker to bypass the FORTIFY_SOURCE protection mechanism, which is designed to detect and prevent format string vulnerabilities by performing additional runtime checks. The flaw essentially creates a scenario where the stack-based buffer allocation can be manipulated to exceed normal bounds, leading to potential stack corruption.
The operational impact of this vulnerability is severe and multifaceted, encompassing both denial of service and potential code execution capabilities. When exploited, the vulnerability can cause system crashes through stack corruption, resulting in denial of service conditions that can disrupt critical services and applications relying on glibc for their operation. More concerning is the potential for arbitrary code execution, which would allow attackers to gain unauthorized control over affected systems. This represents a significant threat to system integrity and security, as the vulnerability can be exploited in applications that use format string functions without proper input validation. The vulnerability's classification under CWE-121 indicates it involves stack-based buffer overflow conditions, while its relationship to the broader category of format string vulnerabilities aligns with ATT&CK technique T1059.007 for command and scripting interpreter usage, as attackers may leverage this to execute malicious code through compromised applications.
Mitigation strategies for this vulnerability require immediate attention and systematic implementation across affected systems. The primary solution involves updating to patched versions of glibc where the alloca function usage has been properly restricted and bounded, ensuring that the SPECS array allocation cannot be manipulated through crafted format strings. System administrators should prioritize patching all affected systems, particularly those running older glibc versions, as the vulnerability exists across multiple versions and affects a fundamental system library. Additional defensive measures include implementing proper input validation in applications that handle user-supplied format strings, using secure alternatives like snprintf instead of sprintf, and employing stack protection mechanisms such as stack canaries and address space layout randomization. Organizations should also consider implementing runtime monitoring and intrusion detection systems to identify potential exploitation attempts, as the vulnerability's exploitation may generate unusual stack allocation patterns that can be detected through proper system monitoring and logging practices.