CVE-2024-46796 is a vulnerability identified in the Linux kernel's SMB (Server Message Block) client implementation, specifically within the CIFS (Common Internet File System) module. The flaw arises from improper handling of reference counting for the @cfile object in the smb2_set_path_size() function. When smb2_compound_op() is invoked with a valid @cfile and returns an -EINVAL error, the code fails to properly reacquire a writable path reference before retrying, leading to a double put (double release) of the @cfile reference. This results in a use-after-free condition, as the reference to the @cfile is dropped prematurely. The vulnerability was detected through Kernel Address Sanitizer (KASAN) testing, which revealed a slab-use-after-free bug during filesystem tests against Windows Server 2022 shares. The bug manifests as a memory corruption issue in detach_if_pending(), triggered by asynchronous CIFS oplock break handling and deferred file closure workqueue processing. The stack traces indicate that the flaw can cause kernel memory corruption, potentially leading to system instability or crashes. Although no public exploits are currently known, the vulnerability affects Linux kernel versions prior to the patch and impacts systems using CIFS/SMB client functionality to mount or interact with Windows SMB shares. The root cause is a logic error in reference management during SMB2 compound operations, which can be triggered by specific filesystem operations such as file truncation or attribute changes over SMB mounts. This vulnerability is particularly relevant for environments where Linux clients access Windows Server SMB shares, a common scenario in mixed OS enterprise networks.

For European organizations, this vulnerability poses a risk primarily to Linux systems that mount SMB shares from Windows servers or other SMB-capable devices. Exploitation could lead to kernel memory corruption, causing system crashes (denial of service) or potentially enabling privilege escalation or arbitrary code execution within the kernel context if combined with other vulnerabilities. This could disrupt critical file sharing services, impacting business operations reliant on cross-platform file access. Organizations in sectors with heavy use of Linux clients accessing Windows file servers—such as finance, manufacturing, and public administration—may face operational disruptions. Additionally, the vulnerability could be leveraged in targeted attacks against Linux endpoints in corporate networks, especially where SMB shares are extensively used for collaboration and data exchange. The lack of known exploits reduces immediate risk, but the potential severity of kernel-level memory corruption warrants prompt attention. The vulnerability also increases the attack surface for advanced persistent threat actors aiming to compromise Linux hosts in European enterprises.

European organizations should prioritize updating their Linux kernels to versions that include the patch fixing CVE-2024-46796 as soon as it becomes available. Until patched, administrators should consider the following specific mitigations: 1) Limit or restrict the use of CIFS/SMB mounts on Linux clients, especially those connecting to Windows Server 2022 or similar SMB shares, to reduce exposure. 2) Employ kernel hardening techniques such as Kernel Address Sanitizer (KASAN) in testing environments to detect similar issues proactively. 3) Monitor kernel logs for KASAN or slab-use-after-free warnings related to CIFS operations, which could indicate attempted exploitation or instability. 4) Implement strict access controls and network segmentation to isolate Linux clients that require SMB access, minimizing lateral movement risk. 5) Use alternative secure file sharing protocols where feasible, such as NFS or SFTP, to reduce reliance on SMB client mounts. 6) Conduct thorough testing of SMB client functionality post-patch deployment to ensure stability and compatibility. These measures, combined with timely patching, will mitigate the risk posed by this vulnerability.