CVE-2025-21906 is a medium-severity vulnerability in the Linux kernel's iwlwifi driver related to improper cleanup of remain-on-channel (ROC) state on failure. The flaw occurs when the firmware fails to start session protection, causing a cleanup function not to execute correctly due to a missing status flag. This can lead to a kernel warning (WARN_ON) because the link remains active when it should have been deactivated.