CVE-2012-3404 in Ubuntu Linux
Summary
by MITRE
The vfprintf function in stdio-common/vfprintf.c in libc in GNU C Library (aka glibc) 2.12 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 (stack corruption and crash) via a format string that uses positional parameters and many format specifiers.
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Analysis
by VulDB Data Team • 03/11/2022
The vulnerability identified as CVE-2012-3404 resides within the GNU C Library's implementation of the vfprintf function, specifically in the stdio-common/vfprintf.c file. This flaw represents a critical issue in the library's handling of format strings that utilize positional parameters alongside multiple format specifiers. The vulnerability affects glibc versions 2.12 and earlier, making it a long-standing weakness that has persisted across multiple releases of the fundamental system library. The issue fundamentally stems from improper buffer length calculation during format string processing, which directly undermines the security mechanisms designed to protect against format string attacks.
The technical flaw manifests when the vfprintf function processes format strings containing positional parameters such as %1$s, %2$s, and so forth, combined with numerous format specifiers. During this processing, the function fails to accurately compute the required buffer size needed to safely store the formatted output. This miscalculation creates a scenario where the FORTIFY_SOURCE protection mechanism, which is designed to detect and prevent format string vulnerabilities by checking buffer boundaries, becomes ineffective. The improper buffer length calculation allows attackers to manipulate the stack layout through carefully crafted format strings that exploit the library's internal memory management.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable more sophisticated attacks. Context-dependent attackers can leverage this flaw to cause stack corruption and subsequent application crashes, effectively creating a reliable method for achieving denial of service against any application linked against the vulnerable glibc version. The vulnerability is particularly dangerous because it bypasses the standard FORTIFY_SOURCE protections that system administrators and developers rely upon for defense-in-depth. Applications using functions like printf, fprintf, or vfprintf that depend on this library component become susceptible to exploitation, making the vulnerability widespread across Unix-like systems where glibc is the standard C library implementation.
Mitigation strategies for CVE-2012-3404 primarily focus on upgrading to patched versions of glibc where the buffer length calculation has been corrected. System administrators should prioritize updating their glibc installations to versions that contain the appropriate fixes, typically glibc 2.13 or later. The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and can be categorized under ATT&CK technique T1059.007 for command and script injection. Additional protective measures include implementing proper input validation, restricting format string usage in applications, and utilizing address space layout randomization (ASLR) and stack canaries to mitigate potential exploitation. Organizations should also consider implementing runtime monitoring to detect unusual format string processing patterns that might indicate exploitation attempts, particularly in systems where updating glibc is not immediately feasible due to compatibility concerns.