CVE-2025-39793: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-39793 is a vulnerability discovered in the Linux kernel's io_uring/memmap functionality, specifically related to casting nr_pages to size_t before shifting operations. The vulnerability was disclosed on September 12, 2025, affecting the Linux kernel's memory management subsystem (NVD).

The vulnerability occurs when the allocated size exceeds UINT_MAX, requiring the mr->nr_pages value to be cast to size_t to prevent overflow. While this issue is typically mitigated by upfront memory size validation and user accounting, systems where root access is utilized may bypass these accounting measures, potentially leading to exploitation (NVD).

The vulnerability primarily affects systems where root access is available, as normal user restrictions (locked_vm settings in the kb to mb range) typically prevent exploitation. However, when root privileges are used, the accounting restrictions are bypassed, potentially leading to memory management issues (NVD).

Ubuntu has released patches for various kernel versions, with most LTS releases being marked as 'Not affected'. However, some versions including Ubuntu 25.04 plucky and specific kernel variants (linux-hwe-6.14, linux-aws-6.14) remain vulnerable and require updates (Ubuntu).