CVE-2006-6304 in Linux
Summary
by MITRE
The do_coredump function in fs/exec.c in the Linux kernel 2.6.19 sets the flag variable to O_EXCL but does not use it, which allows context-dependent attackers to modify arbitrary files via a rewrite attack during a core dump.
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Analysis
by VulDB Data Team • 03/13/2021
The vulnerability described in CVE-2006-6304 resides within the Linux kernel's core dump handling mechanism, specifically in the do_coredump function located in fs/exec.c. This flaw represents a classic race condition vulnerability that exploits the improper handling of file system flags during core dump generation processes. The issue manifests when the kernel sets the O_EXCL flag but fails to utilize it in subsequent file operations, creating a window where malicious actors can manipulate the core dump creation process. The vulnerability is context-dependent, meaning its exploitation requires specific conditions to be met, including the ability to influence the timing of file system operations during core dump generation. This type of vulnerability falls under the broader category of race condition exploits and can be classified as a CWE-362 - Concurrent Execution using Shared Resource with Unprotected Race Condition, which is a fundamental security weakness in concurrent programming models.
The technical implementation of this vulnerability stems from the kernel's core dump subsystem where the O_EXCL flag is set to ensure exclusive access to a file during creation but is subsequently ignored during the actual file writing operations. When a process crashes and the kernel attempts to generate a core dump, it creates a file with the O_EXCL flag to prevent concurrent access, yet fails to enforce this exclusivity during the actual file writing phase. This creates an opportunity for attackers to perform a rewrite attack by creating a symbolic link or manipulating the file system state between the flag setting and the actual file creation. The attack vector leverages the time gap between when the flag is set and when it would be properly enforced, allowing an attacker to substitute the intended core dump file with a malicious file or modify existing files in the system. This vulnerability directly relates to the ATT&CK technique T1059.007 - Command and Scripting Interpreter: Unix Shell, as it can be exploited through shell-based attacks that manipulate core dump processes and file system states.
The operational impact of CVE-2006-6304 extends beyond simple file modification capabilities, as it can potentially enable privilege escalation and system compromise when combined with other attack vectors. Attackers can exploit this vulnerability to overwrite critical system files, modify configuration data, or inject malicious code into the system through the core dump process. The vulnerability affects systems running Linux kernel versions up to and including 2.6.19, representing a significant security risk for any organization using these older kernel versions. The implications are particularly severe in multi-user environments where attackers may have limited access to the system but can leverage this vulnerability to gain unauthorized modifications to system files. The vulnerability can also be exploited in conjunction with other weaknesses to create more sophisticated attack chains, potentially leading to complete system compromise and persistent backdoor access.
Mitigation strategies for this vulnerability primarily focus on kernel version upgrades and proper system hardening measures. Organizations should immediately upgrade to Linux kernel versions 2.6.20 or later where this vulnerability has been addressed through proper implementation of the O_EXCL flag enforcement. System administrators should also implement strict file system permissions and monitoring to detect unauthorized modifications to core dump directories. The use of mandatory access controls such as SELinux or AppArmor can provide additional protection layers by restricting file access patterns during core dump generation. Additionally, regular security audits and monitoring of core dump processes should be implemented to detect potential exploitation attempts. The vulnerability highlights the importance of proper flag validation and enforcement in kernel-level file operations, emphasizing the need for comprehensive testing of concurrent file system operations. Security professionals should also consider implementing intrusion detection systems that monitor for suspicious file creation patterns and unauthorized core dump activities to provide early warning of potential exploitation attempts.