CVE-2019-8790 in Swift
Summary
by MITRE • 10/28/2020
This issue was addresses by updating incorrect URLSession file descriptors management logic to match Swift 5.0. This issue is fixed in Swift 5.1.1 for Ubuntu. Incorrect management of file descriptors in URLSession could lead to inadvertent data disclosure.
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Analysis
by VulDB Data Team • 11/28/2020
The vulnerability identified as CVE-2019-8790 represents a critical flaw in Swift's URLSession implementation that affects file descriptor management within the networking framework. This issue specifically impacts systems running Swift 5.0 and earlier versions, where the URLSession class fails to properly handle file descriptor lifecycle management during network operations. The improper handling occurs when URLSession instances are created and used for downloading or uploading data, particularly when dealing with temporary files and underlying file system resources. The vulnerability stems from a fundamental flaw in how Swift manages the relationship between network operations and the file descriptors that represent the underlying file system resources used for temporary data storage during transfers. This mismanagement creates a scenario where file descriptors may remain open or improperly closed, leading to unintended exposure of sensitive data that was intended to be contained within the scope of network operations.
The technical root cause of this vulnerability lies in the incorrect implementation of file descriptor management within Swift's URLSession framework. When network operations are performed through URLSession, the system creates temporary files to store intermediate data during transfer processes. The flawed logic in Swift 5.0 fails to properly close or release these file descriptors when operations complete, allowing the underlying file system resources to remain accessible to unauthorized processes or users. This creates a data disclosure risk where sensitive information that was meant to be handled securely within the confines of network operations could be accessed by other processes running on the same system. The vulnerability manifests particularly when multiple concurrent network operations occur, as the improper file descriptor management can lead to cross-contamination of temporary files or exposure of file system metadata that might contain sensitive information. The issue is categorized under CWE-200, which deals with improper exposure of sensitive information, and specifically relates to improper resource management within network operation frameworks.
The operational impact of CVE-2019-8790 extends beyond simple data exposure to potentially compromise the integrity and confidentiality of applications that rely on URLSession for network communications. Systems running affected Swift versions may experience unauthorized access to temporary files created during network operations, including potentially sensitive data such as authentication tokens, user credentials, or application-specific information. The vulnerability is particularly concerning in environments where multiple applications or processes share the same file system or where applications are running with elevated privileges. Attackers could exploit this weakness to gain access to temporary files that contain sensitive information, potentially leading to credential theft, data breaches, or further exploitation of the compromised system. The risk is amplified in server-side applications or mobile applications that perform frequent network operations, as the accumulation of improperly managed file descriptors over time could increase the attack surface and create persistent exposure windows.
Mitigation strategies for CVE-2019-8790 focus primarily on updating to the patched version of Swift where the issue has been resolved. Organizations should immediately upgrade to Swift 5.1.1 or later versions that include the corrected URLSession file descriptor management logic. The fix implemented in Swift 5.1.1 addresses the core problem by ensuring proper lifecycle management of file descriptors associated with network operations, including appropriate cleanup and release of temporary file resources. Additionally, system administrators should implement monitoring solutions to detect any unauthorized access to temporary files or unusual file descriptor usage patterns that might indicate exploitation attempts. Security teams should also conduct thorough vulnerability assessments to identify applications built with affected Swift versions and ensure proper patching across all development and production environments. The remediation process should include comprehensive testing to verify that the updated Swift version does not introduce compatibility issues with existing applications while ensuring that network operations properly clean up temporary resources. Organizations should also consider implementing additional security controls such as restricted file system permissions and process isolation to minimize the potential impact even if the vulnerability is not fully patched. This vulnerability demonstrates the importance of proper resource management in networking frameworks and aligns with ATT&CK technique T1071.004 for application layer protocol, emphasizing the need for secure coding practices in network operation implementations.