CVE-2012-3405 in Ubuntu Linux
Summary
by MITRE
The vfprintf function in stdio-common/vfprintf.c in libc in GNU C Library (aka glibc) 2.14 and other versions does not properly calculate a buffer length, which allows context-dependent attackers to bypass the FORTIFY_SOURCE format-string protection mechanism and cause a denial of service (segmentation fault and crash) via a format string with a large number of format specifiers that triggers "desynchronization within the buffer size handling," a different vulnerability than CVE-2012-3404.
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Analysis
by VulDB Data Team • 03/11/2022
The vulnerability described in CVE-2012-3405 represents a critical flaw in the GNU C Library's implementation of the vfprintf function, which serves as a fundamental component in C program execution and string formatting operations. This issue affects glibc versions including 2.14 and other releases, making it a widespread concern across numerous Linux distributions and Unix-like systems. The vulnerability specifically targets the FORTIFY_SOURCE protection mechanism, a security feature designed to detect and prevent format string vulnerabilities by validating buffer boundaries during string operations. When attackers exploit this flaw through carefully crafted format strings containing an excessive number of format specifiers, they can manipulate the internal buffer length calculations to bypass these protective measures.
The technical root cause of this vulnerability lies in the improper buffer length calculation within the stdio-common/vfprintf.c file of glibc. This flaw creates a condition where the library fails to accurately track buffer boundaries when processing complex format strings, leading to a desynchronization between the expected and actual buffer sizes during string formatting operations. The vulnerability is particularly insidious because it operates at the core libc level, meaning that any application relying on standard C library functions for string formatting could be affected. The specific mechanism involves the interaction between format string parsing and buffer management, where the excessive number of format specifiers causes the internal state tracking to become inconsistent, ultimately leading to memory access violations.
From an operational perspective, this vulnerability presents a significant risk to system stability and availability, as it can be exploited to trigger segmentation faults and system crashes through carefully constructed input. Attackers can leverage this flaw to perform denial of service attacks against applications that utilize standard C library formatting functions, potentially affecting web servers, database systems, and other critical infrastructure components. The vulnerability's context-dependent nature means that exploitation requires specific conditions involving format string manipulation, but the impact can be severe enough to cause complete system instability. The flaw represents a deviation from the expected behavior described in CVE-2012-3404, indicating that while related, this vulnerability manifests through a distinct code path involving buffer size handling rather than the more commonly known format string buffer overflow conditions.
The security implications extend beyond simple denial of service, as this vulnerability demonstrates weaknesses in the fundamental security mechanisms that protect against format string attacks. This flaw undermines the effectiveness of FORTIFY_SOURCE, which is a critical defense-in-depth mechanism that relies on proper buffer boundary calculations to detect potential exploits. Organizations using affected glibc versions should consider this vulnerability as a potential entry point for more sophisticated attacks, since bypassing FORTIFY_SOURCE protection can open pathways for additional exploitation techniques. The vulnerability aligns with attack patterns documented in the MITRE ATT&CK framework under process injection and privilege escalation techniques, as compromised applications can be used to gain further system access. Remediation efforts should focus on updating to patched glibc versions, while system administrators should monitor for potential exploitation attempts and ensure that all applications are properly updated to prevent both immediate denial of service conditions and long-term security degradation.
This vulnerability exemplifies the complexity of modern software security, where seemingly minor flaws in core library functions can have cascading effects on entire system architectures. The issue demonstrates how defensive mechanisms like FORTIFY_SOURCE, while valuable, can themselves become targets for exploitation when implementation details contain logical flaws. The vulnerability's classification under CWE-129 and related format string handling categories highlights the ongoing challenges in implementing robust input validation and buffer management in standard library implementations. Organizations should implement comprehensive patch management strategies to address this vulnerability, as the potential for exploitation extends across multiple application types and system configurations. The technical analysis reveals that this flaw represents a fundamental issue in how glibc handles complex format string operations, emphasizing the need for rigorous testing and validation of security mechanisms in core system libraries.