CVE-2021-47394: 
Linux Kernel vulnerability analysis and mitigation

In the Linux kernel, a use-after-free vulnerability (CVE-2021-47394) was discovered in the netfilter nf_tables subsystem. The issue occurs because all get operations are lockless, and the commit_mutex held by nft_rcv_nl_event() is insufficient to prevent parallel GET requests from accessing the table object after synchronize_rcu() (NVD).

The vulnerability stems from a race condition in the nf_tables subsystem where parallel GET requests can perform read-accesses to a table object even after synchronize_rcu(). This occurs because the commit_mutex protection is inadequate for preventing concurrent access. The issue manifests as a use-after-free bug detected by KASAN in the memcmp function. The CVSS v3.1 base score is 7.8 (HIGH) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (NVD).

This vulnerability could allow an attacker with local access to cause a use-after-free condition, potentially leading to privilege escalation, information disclosure, or system crashes. The high CVSS score indicates severe potential impacts on system confidentiality, integrity, and availability (NVD).

The vulnerability has been fixed by unlinking the table first and storing the table objects in on-stack scratch space. The fix was implemented in kernel commit a499b03bf36b0c2e3b958a381d828678ab0ffc5e and backported in commit f65c73d3aabb87d4353e0bc4a718b5ae8c43fd04. Users should upgrade to a patched kernel version to mitigate this vulnerability (Kernel Patch).