CVE-2018-6551 in C Library
Summary
by MITRE
The malloc implementation in the GNU C Library (aka glibc or libc6), from version 2.24 to 2.26 on powerpc, and only in version 2.26 on i386, did not properly handle malloc calls with arguments close to SIZE_MAX and could return a pointer to a heap region that is smaller than requested, eventually leading to heap corruption.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 02/03/2023
The vulnerability identified as CVE-2018-6551 represents a critical heap management flaw within the GNU C Library implementation that affects multiple architectures including powerpc and i386. This issue stems from improper handling of malloc function calls when parameters approach the maximum value of size_t, specifically SIZE_MAX, creating a scenario where the memory allocator fails to provide sufficient heap space as requested. The flaw manifests differently across architectures with powerpc systems affected from glibc version 2.24 through 2.26 and i386 systems only impacted in version 2.26, indicating architecture-specific code paths that were not properly validated during memory allocation operations.
The technical root cause of this vulnerability lies in the malloc implementation's failure to correctly validate and process memory allocation requests that approach system limits. When malloc is called with arguments near SIZE_MAX, the internal heap management logic does not properly account for the maximum possible allocation size, resulting in the allocation function returning a pointer to heap memory that is smaller than the requested amount. This occurs due to integer overflow conditions and insufficient boundary checking within the memory allocation algorithm, creating a condition where memory corruption can occur when applications attempt to use the returned memory region beyond its actual allocated size. The vulnerability specifically targets the heap corruption mechanism rather than direct memory access violations, making it particularly insidious as it can lead to unpredictable behavior and potential exploitation.
The operational impact of CVE-2018-6551 extends beyond simple memory allocation failures to encompass potential system stability and security compromise. Applications utilizing glibc malloc functions with large memory requests near system limits may experience heap corruption that could lead to application crashes, data corruption, or in worst-case scenarios, arbitrary code execution. The vulnerability affects any software relying on standard memory allocation functions, making it particularly dangerous in server environments where memory-intensive applications are common. Attackers could potentially exploit this weakness by crafting specific memory allocation requests that trigger the heap corruption condition, leading to privilege escalation or denial of service scenarios. The vulnerability's impact is amplified by the fact that it affects core system libraries used by virtually all Linux applications, making widespread exploitation possible across multiple software domains.
Mitigation strategies for CVE-2018-6551 require immediate system updates to patched versions of glibc where available. Organizations should prioritize updating their glibc implementations to versions that address the specific heap management flaw in malloc operations near SIZE_MAX boundaries. System administrators should also implement monitoring for applications that make large memory allocation requests, particularly those approaching system limits, to detect potential exploitation attempts. The vulnerability aligns with CWE-122 (Heap-based Buffer Overflow) and can be categorized under ATT&CK technique T1059 (Command and Scripting Interpreter) when exploited through memory corruption attacks, as attackers may attempt to leverage heap corruption to execute malicious code. Additional defensive measures include implementing address space layout randomization (ASLR) and stack canaries to complicate exploitation attempts, while also conducting thorough code reviews of memory allocation patterns within applications to identify potential vulnerable code paths. The remediation process should include comprehensive testing of updated systems to ensure that the patched glibc implementation resolves the heap corruption conditions without introducing regressions in application functionality.