CVE-2016-8605 in Guile
Summary
by MITRE
The mkdir procedure of GNU Guile temporarily changed the process' umask to zero. During that time window, in a multithreaded application, other threads could end up creating files with insecure permissions. For example, mkdir without the optional mode argument would create directories as 0777. This is fixed in Guile 2.0.13. Prior versions are affected.
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Analysis
by VulDB Data Team • 10/28/2022
The vulnerability identified as CVE-2016-8605 resides within the GNU Guile scripting language implementation, specifically affecting the mkdir procedure functionality. This issue represents a classic race condition problem that exploits the temporary manipulation of process permissions during directory creation operations. The flaw manifests when the mkdir procedure temporarily sets the process umask to zero, creating a window of opportunity where concurrent threads can interfere with the permission settings of newly created files or directories. This vulnerability directly impacts the principle of least privilege and proper access control enforcement within multithreaded environments.
The technical implementation of this vulnerability stems from how GNU Guile handles directory creation in multithreaded applications. When the mkdir procedure executes without an explicit mode argument, it temporarily modifies the process umask to zero to ensure directory creation with full permissions. During this brief period when umask is set to zero, other threads within the same process can create files or directories that inherit the insecure permissions. The default behavior creates directories with 0777 permissions, which allows full read, write, and execute access for all users, violating fundamental security principles of access control and file system security. This behavior aligns with CWE-362, which describes race conditions that can lead to security vulnerabilities through improper synchronization of concurrent operations.
The operational impact of this vulnerability extends beyond simple permission misconfiguration to potentially enable privilege escalation and unauthorized access to system resources. In multithreaded applications, malicious or poorly designed threads could exploit this window to create files with insecure permissions, potentially allowing unauthorized users to access sensitive data or system resources. The vulnerability affects all versions of GNU Guile prior to 2.0.13, making it a significant concern for systems running older versions of this scripting language implementation. This issue particularly impacts applications that rely on Guile for system administration tasks, web application backends, or any environment where secure file creation is critical for maintaining system integrity.
The remediation strategy for CVE-2016-8605 involves upgrading to GNU Guile version 2.0.13 or later, which addresses the race condition by properly synchronizing the umask manipulation during directory creation operations. System administrators should prioritize this upgrade across all production environments where GNU Guile is deployed, particularly in multi-threaded applications where concurrent access to file system operations occurs. Organizations should also implement monitoring for any unauthorized file creation with insecure permissions and conduct security audits of applications that utilize Guile to ensure proper implementation of file system access controls. This vulnerability demonstrates the importance of proper synchronization mechanisms in concurrent programming environments and aligns with ATT&CK technique T1068, which covers the exploitation of system vulnerabilities through race conditions and privilege escalation opportunities.