CVE-2017-15670 in C Library
Summary
by MITRE
The GNU C Library (aka glibc or libc6) before 2.27 contains an off-by-one error leading to a heap-based buffer overflow in the glob function in glob.c, related to the processing of home directories using the ~ operator followed by a long string.
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Analysis
by VulDB Data Team • 01/19/2021
The vulnerability identified as CVE-2017-15670 represents a critical heap-based buffer overflow within the GNU C Library that affects systems running glibc versions prior to 2.27. This flaw resides in the glob function implementation within glob.c and specifically manifests when processing home directory expansions using the tilde (~) operator followed by excessively long string sequences. The issue stems from an off-by-one error that allows attackers to write beyond the allocated buffer boundaries, potentially enabling arbitrary code execution or system compromise. The vulnerability is particularly concerning because it operates within a core system library that numerous applications and services depend upon, making it a prime target for exploitation across various attack vectors.
The technical implementation of this vulnerability occurs during the processing of pathname expansion operations where the glob function attempts to resolve home directory references using the ~ operator. When a user provides a path containing a tilde followed by a lengthy string, the function fails to properly validate the length of the resulting expanded path, leading to a buffer overflow condition in heap memory. This off-by-one error specifically affects the boundary checking logic that determines whether the expanded home directory path will fit within the allocated buffer space. The flaw can be triggered through various interfaces including shell commands, file system operations, and application functions that utilize glob pattern matching, making exploitation accessible through multiple attack surfaces. According to CWE standards, this corresponds to CWE-121, heap-based buffer overflow, and represents a classic memory safety vulnerability that has been historically exploited in privilege escalation scenarios.
The operational impact of CVE-2017-15670 extends far beyond simple denial of service conditions, as it can enable remote code execution and privilege escalation attacks. Attackers can exploit this vulnerability by crafting malicious input containing extended tilde expansions that cause the buffer overflow, potentially allowing them to overwrite critical heap metadata or execute arbitrary code with the privileges of the affected process. The vulnerability affects systems where applications rely on glob pattern matching for file operations, including shell utilities, system administration tools, and network services that process user-provided paths. This makes it particularly dangerous in multi-user environments where unprivileged users could potentially exploit the vulnerability to gain elevated privileges or compromise system integrity. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting the execution of malicious code through memory corruption vulnerabilities.
Mitigation strategies for CVE-2017-15670 require immediate system updates to glibc version 2.27 or later, which contain the necessary patches to address the buffer overflow condition. Organizations should prioritize patching all systems running affected glibc versions, particularly those hosting services that process user input through glob pattern matching operations. Additional defensive measures include implementing input validation controls that limit the length of user-provided paths, disabling unnecessary shell features that utilize glob expansion, and monitoring system logs for suspicious pattern matching operations. Security teams should also consider implementing runtime protections such as stack canaries, address space layout randomization, and heap integrity checking mechanisms to reduce the effectiveness of potential exploitation attempts. System administrators must conduct comprehensive vulnerability assessments to identify all applications and services that might be vulnerable to this specific heap overflow condition, ensuring that the patching process covers all potential attack surfaces within their infrastructure.