Buildroot before 0b2967e lacks the sticky bit for the /dev/shm directory. A fix was released in 2024.02.2.
https://www.openwall.com/lists/oss-security/2024/04/11/13
https://github.com/buildroot/buildroot/commit/0b2967e15800421efbdfe3a7a6061cf6bd84134d
http://www.openwall.com/lists/oss-security/2024/05/07/4