CVE-2025-40126: 
Linux Debian vulnerability analysis and mitigation

CVE-2025-40126 is a vulnerability discovered in the Linux kernel affecting the SPARC architecture, specifically related to exception reporting in copy{fromto}_user functions for UltraSPARC. The vulnerability was disclosed on November 12, 2025 (NVD).

The vulnerability involves exception handlers on user-space memory references in copyfromuser and copytouser functions. These handlers were designed to return from their respective functions and calculate remaining bytes for copying using current register contents. The issue stems from incorrect calculations that affect the return values of copyfromuser and copytouser functions in faulting cases, though the behavior of memcpy remains unchanged (NVD).

The vulnerability affects various Linux distributions and kernel versions, with Ubuntu assigning it a Medium priority rating. Multiple Linux kernel packages across different versions are marked as vulnerable, including several LTS releases (Ubuntu).

The vulnerability has been addressed in the Linux kernel version 6.1.158-1~deb11u1 for Debian 11 bullseye, which includes fixes for this and numerous other security issues (Debian).