CVE-2025-40055 in Linux
Summary
by MITRE • 10/28/2025
In the Linux kernel, the following vulnerability has been resolved:
ocfs2: fix double free in user_cluster_connect()
user_cluster_disconnect() frees "conn->cc_private" which is "lc" but then the error handling frees "lc" a second time. Set "lc" to NULL on this path to avoid a double free.
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Analysis
by VulDB Data Team • 05/20/2026
The vulnerability identified as CVE-2025-40055 represents a critical double free error within the Linux kernel's ocfs2 filesystem implementation. This flaw manifests in the user_cluster_connect() function where improper memory management leads to the same memory block being freed twice, creating a potential exploitation vector for denial of service or arbitrary code execution. The issue specifically affects the ocfs2 cluster communication subsystem that handles distributed file system operations across multiple nodes in a cluster environment. The vulnerability occurs when the user_cluster_disconnect() function processes connection cleanup, where the connection private data structure lc is freed during normal operation but subsequently freed again during error handling paths. This memory management error violates fundamental security principles and creates an unstable system state that could be exploited by malicious actors.
The technical implementation of this vulnerability stems from a classic memory management flaw where the lc pointer is not properly nullified after its initial free operation in the user_cluster_disconnect() function. According to CWE-415, this represents an explicit double free condition that occurs when a program attempts to free the same memory block twice. The error handling path in the ocfs2 subsystem fails to account for the fact that lc has already been freed, leading to a second free operation on the same memory location. This type of vulnerability is particularly dangerous in kernel space because it can lead to memory corruption that affects system stability and potentially allows privilege escalation. The ATT&CK framework categorizes this under T1068, which involves exploiting local privilege escalation vulnerabilities, as the kernel memory corruption could enable attackers to gain elevated system privileges.
The operational impact of CVE-2025-40055 extends beyond simple system crashes, potentially enabling more sophisticated attacks depending on the execution environment and system configuration. When the double free occurs, it can corrupt the kernel's memory allocator's internal data structures, leading to unpredictable behavior including system panics, data corruption, or in worst-case scenarios, remote code execution. The vulnerability affects systems running the Linux kernel with ocfs2 filesystem support, particularly those in high-availability cluster environments where distributed file system operations are common. The exploitability of this vulnerability depends on the attacker's ability to trigger the specific code path that leads to the double free condition, typically through cluster communication operations or file system access patterns. Organizations using ocfs2 in production environments face significant risk as this vulnerability could be leveraged to disrupt critical services or gain unauthorized access to cluster resources.
Mitigation strategies for CVE-2025-40055 primarily focus on applying the official kernel patch that addresses the double free condition by setting the lc pointer to NULL after its initial free operation. System administrators should prioritize updating their kernel versions to include the patched code that prevents the second free operation from occurring. Additionally, implementing proper memory management practices in custom kernel modules or applications that interact with ocfs2 filesystems can help prevent similar issues. Monitoring for unusual system behavior or kernel panic reports may help detect exploitation attempts, while network segmentation and access controls can limit the potential impact of successful exploitation. The fix aligns with best practices for kernel memory management and follows established security guidelines for preventing heap corruption vulnerabilities. Organizations should also conduct thorough testing of kernel updates in staging environments to ensure compatibility with existing ocfs2 cluster configurations before deploying patches to production systems.