CVE-2015-1473 in C Library
Summary
by MITRE
The ADDW macro in stdio-common/vfscanf.c in the GNU C Library (aka glibc or libc6) before 2.21 does not properly consider data-type size during a risk-management decision for use of the alloca function, which might allow context-dependent attackers to cause a denial of service (segmentation violation) or overwrite memory locations beyond the stack boundary via a long line containing wide characters that are improperly handled in a wscanf call.
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Analysis
by VulDB Data Team • 03/11/2022
The vulnerability identified as CVE-2015-1473 resides within the GNU C Library implementation of the ADDW macro in stdio-common/vfscanf.c file. This flaw represents a classic buffer management issue that affects the fundamental string parsing capabilities of glibc. The vulnerability specifically impacts the wscanf function family which processes wide character input streams, making it particularly dangerous in applications that handle internationalized text or user input containing multibyte characters. The flaw stems from improper consideration of data-type sizing during memory allocation decisions, creating a scenario where the library makes unsafe assumptions about stack memory usage when processing wide character sequences.
The technical exploitation of this vulnerability occurs when the ADDW macro fails to accurately assess the memory requirements for wide character processing, leading to incorrect use of the alloca function. The alloca function allocates memory on the stack and is particularly sensitive to stack boundary calculations. When processing long lines containing wide characters, the macro's decision-making process regarding stack allocation becomes flawed, potentially causing stack corruption or segmentation violations. This issue manifests when the library attempts to handle wide character sequences that exceed normal processing boundaries, creating a condition where memory beyond the intended stack allocation gets overwritten.
The operational impact of CVE-2015-1473 extends beyond simple denial of service to potentially enable arbitrary code execution in certain contexts. Attackers can craft malicious input streams containing specially formatted wide character sequences that trigger the flawed memory allocation logic. This vulnerability affects systems running glibc versions prior to 2.21, making it particularly relevant for older Linux distributions and embedded systems. The risk is context-dependent as the vulnerability requires specific input patterns that trigger the problematic code path within the wscanf family functions, but once triggered, the consequences can be severe. The vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and represents a classic example of improper handling of memory allocation decisions.
Systems utilizing applications that depend on glibc for wide character processing are particularly vulnerable, including web servers, database systems, and any application that processes user input containing wide character sequences. The attack vector typically involves feeding specially crafted input to applications that use wscanf or related wide character functions, potentially leading to system crashes or more severe exploitation outcomes. Organizations should consider implementing input validation and sanitization measures as temporary mitigations while planning for proper glibc updates. The vulnerability also relates to ATT&CK technique T1059 which involves executing malicious code through command-line interfaces, as exploitation may occur through command-line input processing. Remediation requires updating to glibc version 2.21 or later, which includes proper bounds checking and corrected memory allocation logic for wide character processing. Additionally, security teams should monitor for applications that may be indirectly affected through shared library dependencies and ensure comprehensive testing of input handling routines in all affected systems.