CVE-2017-17426 in C Library
Summary
by MITRE
The malloc function in the GNU C Library (aka glibc or libc6) 2.26 could return a memory block that is too small if an attempt is made to allocate an object whose size is close to SIZE_MAX, potentially leading to a subsequent heap overflow. This occurs because the per-thread cache (aka tcache) feature enables a code path that lacks an integer overflow check.
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Analysis
by VulDB Data Team • 01/17/2023
The vulnerability identified as CVE-2017-17426 represents a critical heap management flaw within the GNU C Library that affects systems running glibc version 2.26 and potentially earlier versions. This issue resides in the malloc implementation where the library fails to properly validate memory allocation requests that approach the maximum possible size limit. The vulnerability specifically manifests when attempting to allocate memory objects whose size is near SIZE_MAX, which is the theoretical maximum value for size_t data types on the system. The flaw stems from the introduction of the per-thread cache mechanism in glibc 2.26, which was designed to improve memory allocation performance by reducing contention in multi-threaded applications. However, this optimization introduced a critical oversight in the integer overflow checking mechanisms that are essential for preventing memory corruption vulnerabilities.
The technical exploitation of this vulnerability occurs through a specific code path that bypasses normal integer overflow checks within the malloc function. When a program attempts to allocate a memory block approaching SIZE_MAX, the tcache feature creates a scenario where the allocation logic fails to detect that the requested size would exceed the available memory space. This oversight allows the malloc function to return a memory block that is smaller than requested, effectively creating a situation where subsequent operations on the allocated memory could overflow into adjacent memory regions. The vulnerability directly relates to CWE-192, which describes integer overflow conditions that can lead to memory corruption, and also maps to ATT&CK technique T1059.007 for command and scripting interpreter usage in exploitation contexts. The flaw is particularly dangerous because it can be leveraged to execute arbitrary code through heap-based buffer overflows, where attackers manipulate the allocation process to overwrite critical memory structures.
The operational impact of CVE-2017-17426 extends across numerous system components and applications that rely on standard memory allocation functions. Any software running on affected systems, including web servers, database applications, and network services, becomes potentially vulnerable to memory corruption attacks. The vulnerability can be exploited by attackers who craft specific allocation requests that trigger the problematic code path, potentially leading to privilege escalation or remote code execution in vulnerable applications. System administrators and security professionals must recognize that this vulnerability affects not just individual applications but the underlying memory management infrastructure that all software depends upon. The risk is particularly elevated in environments where applications perform dynamic memory allocation with large or untrusted input sizes, as these scenarios create ideal conditions for triggering the heap overflow condition. The vulnerability also impacts the broader security ecosystem by potentially compromising the integrity of memory management operations that are fundamental to system stability and security.
Mitigation strategies for CVE-2017-17426 primarily involve updating to patched versions of glibc where the integer overflow checks have been restored and properly implemented. Organizations should prioritize immediate deployment of glibc version 2.27 or later, which includes the necessary fixes to address the tcache memory allocation flaw. System administrators should also implement monitoring for unusual allocation patterns that might indicate exploitation attempts, particularly focusing on applications that handle large memory requests or process untrusted input data. Additional protective measures include enabling address space layout randomization and other memory protection mechanisms to complicate exploitation attempts. The vulnerability highlights the importance of thorough testing of performance optimization features, particularly those that modify core memory management functions, and demonstrates the critical need for comprehensive security reviews of system libraries that serve as foundational components for all software execution. Security teams should also consider implementing application sandboxing and memory access controls to limit the potential impact of successful exploitation attempts, while maintaining awareness of related vulnerabilities that might exist in other system components that depend on the same memory management infrastructure.