CVE-2023-0459: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-0459 is a vulnerability discovered in 64-bit versions of the Linux kernel where copyfromuser does not implement the _uaccessbeginnospec, allowing a user to bypass the "accessok" check. The vulnerability was discovered by Jordy Zomer and Alexandra Sandulescu and affects various Linux distributions (Ubuntu).

The vulnerability stems from a speculative execution issue in the Linux kernel's copyfromuser function. The results of "access_ok()" can be mis-speculated, allowing speculative execution even with invalid from/size combinations. This could potentially lead to information leakage through cache side-effects when userspace passes a pointer that points to kernel addresses (Linux Commit). The vulnerability has been assigned a CVSS 3 Severity Score of 5.5 (Medium) (Ubuntu).

The vulnerability could allow a local attacker to expose sensitive information from kernel memory through speculative execution side-channels. When combined with code that has cache side-effects, it could enable userspace to infer kernel data values (Linux Commit).

The issue has been fixed by adding a speculation barrier to the common copyfromuser() code to prevent mis-speculated values after the copy. The fix was implemented in commit 74e19ef0ff8061ef55957c3abd71614ef0f42f47. Various Linux distributions have released patches to address this vulnerability. Users are recommended to upgrade their systems to the patched versions (Linux Commit, Ubuntu).