CVE-2024-36943 is a vulnerability identified in the Linux kernel related to the handling of page table entries (PTEs) during memory management operations, specifically in the fs/proc/task_mmu subsystem. The vulnerability arises from a race condition in the function make_uffd_wp_pte(), which modifies the protection bits of a PTE to mark it as write-protected for userfaultfd (uffd) handling. The original code sequence first retrieved the PTE using ptep_get(), then started modification with ptep_modify_prot_start(), applied the write-protect modification, and finally committed the change with ptep_modify_prot_commit(). However, between the initial retrieval and the start of modification, another thread could access or dirty the PTE, causing a loss of the 'young' or 'dirty' bits that track page usage and modification. This loss of information can lead to incorrect memory management behavior, potentially causing data corruption or system instability. The fix involves changing the sequence to start the modification atomically with ptep_modify_prot_start(), which both retrieves and clears the PTE atomically, then applying the write-protect modification, and committing the change. This prevents any race condition where another thread could interfere between steps, ensuring that any access after the start of modification sees an invalid PTE and triggers a fault, preserving memory consistency and correctness. The vulnerability affects specific Linux kernel versions identified by commit hashes and was published on May 30, 2024. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations, this vulnerability could impact systems running affected Linux kernel versions, particularly those using userfaultfd mechanisms or relying on precise memory management for performance or security. The loss of 'young' or 'dirty' bits during PTE modification could lead to subtle memory corruption, data integrity issues, or system crashes, which in critical infrastructure or enterprise environments could disrupt services or lead to data loss. Systems with high concurrency and multi-threaded workloads are more susceptible to triggering this race condition. Although no active exploitation is known, the vulnerability could be leveraged in targeted attacks to cause denial of service or to bypass memory protection mechanisms, potentially aiding privilege escalation or sandbox escape attempts. European organizations in sectors such as finance, telecommunications, cloud service providers, and government agencies that heavily depend on Linux-based servers and infrastructure should consider this a significant risk to system stability and security.

Organizations should promptly apply the official Linux kernel patches that address CVE-2024-36943, ensuring that all affected systems are updated to kernel versions containing the fix. Given the technical nature of the fix, it is critical to verify that kernel updates are tested in staging environments to avoid unintended side effects. For environments where immediate patching is not feasible, monitoring for unusual system crashes or memory faults related to userfaultfd operations can help detect potential exploitation attempts. Additionally, limiting the use of userfaultfd to trusted applications and minimizing concurrent access to memory management operations can reduce exposure. Security teams should also review system configurations and kernel parameters related to memory management and concurrency to harden systems. Finally, maintaining robust backup and recovery procedures will mitigate the impact of any data corruption or system instability resulting from this vulnerability.