CVE-2017-15804 in C Library
Summary
by MITRE
The glob function in glob.c in the GNU C Library (aka glibc or libc6) before 2.27 contains a buffer overflow during unescaping of user names with the ~ operator.
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Analysis
by VulDB Data Team • 01/04/2023
The vulnerability identified as CVE-2017-15804 represents a critical buffer overflow flaw within the GNU C Library's glob function implementation. This issue specifically affects the handling of user names when the tilde (~) operator is used in path expansion operations. The flaw exists in the glob.c file where the library processes shell-style pattern matching operations, particularly when expanding user home directories. The vulnerability manifests during the unescaping process of user names, where insufficient bounds checking allows malicious input to overwrite adjacent memory regions. This type of buffer overflow vulnerability falls under the Common Weakness Enumeration category CWE-121, which describes unsafe buffer access conditions that can lead to arbitrary code execution or system compromise.
The technical exploitation of this vulnerability occurs when applications relying on glibc's glob function process user-supplied input containing tilde-expanded paths. Attackers can craft malicious input strings that cause the glob function to write beyond the allocated buffer boundaries during the unescaping of user names. The overflow typically occurs when the function attempts to expand a user name prefixed with the ~ character, such as ~/path or ~username/path, without proper validation of the resulting string length against the allocated buffer capacity. This flaw is particularly dangerous because it can be triggered through various application interfaces that utilize glob pattern matching, including shell utilities, configuration parsers, and system administration tools that depend on standard C library functions for path expansion.
The operational impact of CVE-2017-15804 extends across numerous Linux distributions and Unix-like systems that utilize glibc versions prior to 2.27. Applications that process user input through glob pattern matching operations become vulnerable to remote code execution or denial of service conditions when exploited. The vulnerability can be leveraged in scenarios where user-provided paths are processed through glob functions, such as in web applications handling file operations, system utilities processing configuration files, or command-line tools that support shell expansion features. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter execution, as it can be used to bypass security controls and execute arbitrary code through malformed input processing. The attack surface is broad given that glibc is fundamental to most Unix-like systems and numerous applications depend on its standard library functions.
Mitigation strategies for CVE-2017-15804 primarily focus on updating glibc to version 2.27 or later, which contains the necessary patches to address the buffer overflow condition. System administrators should prioritize patching affected systems, particularly those running older versions of glibc that are still in production use. Additionally, input validation measures can help reduce exploitation risk by sanitizing user-provided paths before they are processed through glob functions. Organizations should also consider implementing runtime protections such as stack canaries, address space layout randomization, and non-executable stack segments to make exploitation more difficult. The vulnerability demonstrates the importance of maintaining up-to-date system libraries and highlights the critical nature of proper bounds checking in C library implementations. Security monitoring should include detection of unusual glob function usage patterns and input processing anomalies that might indicate attempted exploitation of this or similar buffer overflow vulnerabilities.