CVE-2021-47238: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47238 is a memory leak vulnerability discovered in the Linux kernel's IPv4 multicast implementation. The issue was specifically identified in the ip_mc_add1_src function within the IGMP (Internet Group Management Protocol) subsystem. The vulnerability was disclosed on May 21, 2024, and affects the Linux kernel's networking stack (NVD).

The vulnerability stems from a regression introduced by commit 24803f38a5c0 which removed the ip_mc_clear_src() call in ip_mc_destroy_dev(). The issue occurs because ip_mc_clear_src() called in igmpv3_clear_delrec() doesn't properly release in_dev->mc_list->sources, and RCU_INIT_POINTER() assigns NULL to dev->ip_ptr. This results in in_dev being inaccessible through inetdev_by_index(), preventing the proper release of in_dev->mc_list->sources by ip_mc_del1_src() during socket closure (Kernel Commit).

The vulnerability results in a memory leak when handling IPv4 multicast operations. The leaked memory was identified as an unreferenced object of size 32 bytes, which could accumulate over time and potentially lead to resource exhaustion. According to CISA's assessment, this vulnerability has been assigned a CVSS v3.1 Base Score of 5.5 (Medium) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD).

The vulnerability can be triggered through normal system operations involving IPv4 multicast functionality, specifically when closing sockets that were part of multicast groups. The issue was discovered and reported by Hulk Robot through system testing (Kernel Commit).

The vulnerability has been fixed by reintroducing the ip_mc_clear_src() call in ip_mc_destroy_dev() to properly free in_dev->mc_list->sources. The fix was implemented in the Linux kernel through commit d8e2973029b8b2ce477b564824431f3385c77083 (Kernel Commit).