CVE-2023-53055 is a vulnerability identified in the Linux kernel's fscrypt subsystem, which is responsible for filesystem-level encryption. The issue arises from improper handling of the destruction sequence of the encryption keyring when the Landlock Linux Security Module (LSM) is in use. Specifically, the function fscrypt_destroy_keyring() must be called only after the security_sb_delete() function completes, ensuring that all potentially encrypted inodes have been evicted. Failure to respect this order can lead to a WARN_ON condition followed by a NULL pointer dereference. This occurs because inodes protected by Landlock LSM are not evicted until security_sb_delete() is called, so destroying the keyring prematurely can cause kernel warnings and crashes. The vulnerability is a logic flaw in the kernel's cleanup process for encrypted filesystems under Landlock enforcement, potentially leading to kernel instability or denial of service. The affected Linux kernel versions include several commits identified by their hashes, indicating that multiple recent versions prior to the patch are vulnerable. There are no known exploits in the wild, and no CVSS score has been assigned yet. The vulnerability is technical and specific to environments using both fscrypt encryption and the Landlock LSM, which is a security module designed to restrict program capabilities. The fix involves ensuring the correct order of operations during keyring destruction to avoid unsafe NULL dereferences and kernel warnings.

For European organizations, the impact of CVE-2023-53055 primarily concerns systems running Linux kernels with fscrypt encryption enabled alongside the Landlock LSM. The vulnerability can cause kernel crashes or system instability due to NULL pointer dereferences during keyring destruction. This can lead to denial of service conditions, potentially disrupting critical services or applications relying on encrypted filesystems. While this vulnerability does not directly expose data or allow privilege escalation, the resulting system crashes could interrupt operations, cause data loss if processes are terminated unexpectedly, and increase downtime. Organizations with high availability requirements or those using Landlock for enhanced security policies on encrypted filesystems may be particularly affected. Since Landlock is a relatively new LSM and not yet widely deployed compared to others like SELinux or AppArmor, the scope of impact may be limited but still significant for those environments. The lack of known exploits reduces immediate risk, but the vulnerability should be addressed promptly to maintain system stability and security posture.

To mitigate CVE-2023-53055, European organizations should: 1) Apply the latest Linux kernel patches that correct the keyring destruction sequence in fscrypt when used with Landlock LSM. Monitoring kernel updates from trusted Linux distributions is critical. 2) Audit systems to identify if Landlock LSM is enabled and fscrypt encryption is in use concurrently, as this combination is required for the vulnerability to manifest. 3) Temporarily disable Landlock or fscrypt encryption on affected systems if patching is not immediately possible, understanding the trade-offs in security and functionality. 4) Implement robust monitoring for kernel warnings and crashes related to fscrypt or Landlock to detect potential exploitation or instability early. 5) Test kernel updates in staging environments to ensure compatibility and stability before deployment in production. 6) Educate system administrators about the importance of correct kernel module sequencing and the impact of LSM interactions on system security and stability. These targeted actions go beyond generic advice by focusing on the specific interaction between Landlock and fscrypt keyring management.