CVE-2018-6485 in C Library
Summary
by MITRE
An integer overflow in the implementation of the posix_memalign in memalign functions in the GNU C Library (aka glibc or libc6) 2.26 and earlier could cause these functions to return a pointer to a heap area that is too small, potentially leading to heap corruption.
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Analysis
by VulDB Data Team • 02/03/2023
The vulnerability identified as CVE-2018-6485 represents a critical integer overflow flaw within the GNU C Library implementation of memory allocation functions. This issue specifically affects the posix_memalign function and related memalign implementations in glibc versions 2.26 and earlier, creating a dangerous condition where memory allocation operations can produce incorrectly sized heap allocations. The flaw stems from inadequate input validation and overflow handling during the calculation of memory block sizes, allowing malicious inputs to trigger unexpected behavior in memory management operations. This vulnerability operates at the core of system memory handling mechanisms, potentially compromising the integrity of heap-based data structures and creating opportunities for exploitation.
The technical implementation of this vulnerability involves an integer overflow condition that occurs when the posix_memalign function processes allocation requests with specific parameter values. When the requested alignment and size parameters combine in certain ways, the internal arithmetic operations exceed the maximum representable value for the integer type used in the calculation. This overflow results in a truncated or wrapped value that is subsequently used to determine the actual heap allocation size. The resulting pointer points to memory regions that are significantly smaller than required, creating a condition where subsequent memory operations can overwrite adjacent heap data structures or corrupt memory layout. This flaw aligns with CWE-190, Integer Overflow or Wraparound, which specifically addresses issues where integer arithmetic operations produce results that exceed the range of the data type used to store them.
The operational impact of CVE-2018-6485 extends beyond simple memory corruption, as it creates a foundation for more sophisticated attacks within the system. Applications utilizing the affected glibc versions become vulnerable to heap-based memory corruption, which can be exploited to achieve arbitrary code execution or denial of service conditions. Attackers can craft specific allocation requests that trigger the integer overflow, potentially leading to controlled heap corruption that allows for information disclosure, privilege escalation, or system instability. The vulnerability affects any software stack relying on glibc for memory management, making it particularly dangerous in environments where multiple applications are running with varying levels of privilege. This type of vulnerability is categorized under ATT&CK technique T1068, Exploitation for Privilege Escalation, as heap corruption can enable attackers to gain elevated system privileges.
Mitigation strategies for CVE-2018-6485 primarily focus on upgrading to patched versions of glibc where the integer overflow has been properly addressed through improved input validation and overflow detection mechanisms. System administrators should prioritize updating all affected systems to glibc versions 2.27 or later, where the vulnerability has been resolved through proper integer bounds checking and overflow prevention measures. Additionally, implementing runtime protections such as address space layout randomization and stack canaries can help reduce the effectiveness of exploitation attempts. The vulnerability demonstrates the importance of proper integer arithmetic handling in system libraries and underscores the need for comprehensive security testing of core system components. Organizations should conduct thorough vulnerability assessments to identify all systems running affected glibc versions and implement immediate remediation measures to prevent potential exploitation. The fix typically involves strengthening the validation logic in memory allocation functions to prevent overflow conditions and ensuring that calculated memory sizes remain within acceptable bounds before proceeding with heap allocation operations.