CVE-2018-8086 in C Library
Summary
by MITRE
The basename implementation in string/basename.c in the GNU C Library (aka glibc or libc6) 2.26 allows attackers to cause a denial of service (segmentation fault), within the assembly code for strrchr, via a crafted argument.
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Analysis
by VulDB Data Team • 01/12/2020
The vulnerability identified as CVE-2018-8086 resides within the GNU C Library implementation of the basename function, specifically in the string/basename.c file of glibc version 2.26. This flaw represents a critical security issue that affects systems relying on the standard C library for file path manipulation operations. The vulnerability manifests when the basename function processes a crafted argument that triggers improper handling within the underlying strrchr assembly code implementation. Such a flaw demonstrates the inherent risks present in low-level system libraries where a single implementation error can cascade into system-wide stability issues. The vulnerability is particularly concerning because it affects the fundamental file path processing capabilities that numerous applications and system utilities depend upon for proper operation.
The technical root cause of this vulnerability stems from improper bounds checking and memory access handling within the strrchr function's assembly implementation. When the basename function receives a maliciously crafted input, it passes this argument through to strrchr which then attempts to process it without adequate validation of the input boundaries. This leads to a segmentation fault occurring within the assembly code execution context, causing the process to crash and resulting in a denial of service condition. The flaw specifically impacts the way the assembly code handles memory references and string traversal operations, where insufficient input validation allows for invalid memory access patterns. This type of vulnerability aligns with CWE-125: Out-of-bounds Read and CWE-787: Out-of-bounds Write, as the improper memory handling leads to unauthorized memory access patterns that cause system instability. The assembly level nature of the flaw makes it particularly challenging to detect and mitigate through high-level code analysis alone.
The operational impact of CVE-2018-8086 extends far beyond simple application crashes, as it affects the core system stability of any environment utilizing glibc 2.26 or earlier versions. Any application that relies on basename or related string manipulation functions becomes vulnerable to this denial of service attack, potentially affecting system services, user applications, and critical infrastructure components. The vulnerability can be exploited by attackers who craft specific input parameters that trigger the faulty assembly code path, leading to system-wide service disruption. This attack vector is particularly dangerous in multi-user environments or server configurations where multiple processes may be simultaneously affected by a single malicious input. The vulnerability's impact is amplified by the widespread use of glibc across Unix-like systems, making it a prime target for exploitation in environments where denial of service attacks are preferred over more complex compromise techniques. From an ATT&CK framework perspective, this vulnerability maps to T1499.004: Endpoint Denial of Service, representing a method of disrupting system services through memory corruption techniques.
Mitigation strategies for CVE-2018-8086 primarily focus on immediate system updates and patches provided by the GNU project and affected vendors. System administrators should prioritize upgrading to glibc versions 2.27 or later, where the vulnerability has been resolved through proper bounds checking and memory access validation in the strrchr implementation. Additionally, organizations should implement input validation measures at application layers to sanitize any user-provided arguments before they reach the basename function. Network-level protections can include implementing rate limiting and input filtering mechanisms to prevent exploitation attempts, while monitoring systems should be configured to detect unusual process termination patterns that may indicate exploitation attempts. The vulnerability highlights the importance of maintaining current system libraries and implementing comprehensive security testing procedures, particularly for low-level system components that form the foundation of operating system functionality. Organizations should also consider implementing intrusion detection systems that can identify patterns consistent with exploitation attempts targeting memory corruption vulnerabilities in system libraries.