CVE-2021-3347: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-3347 was discovered in the Linux kernel through version 5.10.11. The vulnerability involves a kernel stack use-after-free condition during fault handling in PI (Priority Inheritance) futexes, allowing local users to execute code in the kernel (NVD, Debian). The issue was identified and patched in January 2021, addressing a longstanding bug that dated back to 2008 (OSS Security).

The vulnerability stems from a condition where the user space part of the PI futex is not writeable, causing the kernel to return with inconsistent state. This inconsistency can result in a use-after-free of a task's kernel stack. The issue has been assigned a CVSS v3.1 Base Score of 7.8 (HIGH) with the vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (NVD). The vulnerability specifically affects the Priority Inheritance futex implementation, which is a fast, lightweight kernel-assisted locking primitive for user-space applications (OSS Security).

When successfully exploited, this vulnerability could allow an unprivileged local user to crash the kernel (resulting in denial of service), execute arbitrary code in kernel context, or escalate privileges. The vulnerability affects the kernel's ability to maintain consistent state between user space and kernel space operations on PI futexes (NetApp, Debian).

The primary mitigation is to update to patched kernel versions. The fix establishes consistent kernel state which makes future operations on the futex fail when user space and kernel space states are inconsistent. This is considered acceptable because PI futexes fundamentally require a functional RW mapping (OSS Security). Multiple Linux distributions have released patches, including Debian (4.19.171-2), Fedora 32 (5.10.12-100.fc32), and Fedora 33 (5.10.12-200.fc33) (Debian, Fedora).