CVE-2008-3833 in Linux
Summary
by MITRE
The generic_file_splice_write function in fs/splice.c in the Linux kernel before 2.6.19 does not properly strip setuid and setgid bits when there is a write to a file, which allows local users to gain the privileges of a different group, and obtain sensitive information or possibly have unspecified other impact, by splicing into an inode in order to create an executable file in a setgid directory, a different vulnerability than CVE-2008-4210.
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Analysis
by VulDB Data Team • 08/18/2019
The vulnerability described in CVE-2008-3833 represents a critical privilege escalation flaw within the Linux kernel's file system operations, specifically affecting versions prior to 2.6.19. This issue resides in the generic_file_splice_write function located in fs/splice.c, which handles the splicing of data between file descriptors. The core problem manifests when local users perform write operations to files through splice operations, creating a scenario where setuid and setgid bits are not properly stripped from the target file. This failure in privilege management creates a pathway for attackers to exploit the system's security model and gain elevated privileges. The vulnerability operates through a sophisticated attack vector that leverages the splice system call to manipulate file permissions in ways that bypass normal security checks.
The technical flaw stems from improper handling of file permission bits during splice operations, specifically the failure to strip setuid and setgid attributes when writing to files. When a user splices data into an inode within a setgid directory, the system should ensure that any executable file created inherits the proper group ownership while losing the setuid/setgid bits that would otherwise grant elevated privileges. However, the kernel's implementation fails to perform this critical cleanup operation, allowing the original setgid permissions to persist. This creates a situation where the resulting executable file maintains the group privileges of the setgid directory, enabling local users to effectively gain the privileges of a different group without proper authentication or authorization. The flaw is particularly dangerous because it operates at the kernel level, making it difficult to detect and exploit without deep understanding of the system's internal operations.
The operational impact of this vulnerability extends beyond simple privilege escalation, potentially enabling local users to access sensitive information and execute arbitrary code with elevated privileges. Attackers can exploit this weakness by creating executable files in setgid directories, which then run with the privileges of the directory's group owner rather than the user who created them. This opens up possibilities for information disclosure, as the elevated privileges may provide access to files and resources that would normally be restricted. Additionally, the vulnerability could allow for unspecified other impacts including system compromise, data corruption, or further exploitation of related vulnerabilities. The attack requires local system access but does not need network connectivity, making it particularly concerning for environments where local access cannot be strictly controlled or monitored. Security researchers have noted that this vulnerability operates differently from CVE-2008-4210, indicating a distinct exploitation pathway that affects the kernel's file system handling mechanisms.
This vulnerability aligns with CWE-276, which addresses improper privilege management in software systems, and represents a classic case of insufficient privilege checking in kernel space operations. From an ATT&CK framework perspective, this flaw maps to privilege escalation techniques, specifically T1068 which involves exploiting vulnerabilities to gain elevated privileges. The vulnerability demonstrates how kernel-level flaws can create persistent security issues that affect system integrity and confidentiality. Organizations should prioritize patching systems running Linux kernel versions before 2.6.19, as this vulnerability represents a serious threat to system security. The fix implemented in kernel version 2.6.19 properly addresses the issue by ensuring that setuid and setgid bits are correctly stripped during splice write operations, thereby preventing unauthorized privilege escalation through this specific attack vector. Regular security audits and kernel updates remain critical for maintaining system security against similar vulnerabilities that may arise from improper privilege handling in core system components.