CVE-2026-23274: In the Linux kernel, the following vulnerability has been resolved: netfilter: xt_IDLETIMER: reject rev0 reuse of ALARM

A vulnerability in the Linux kernel's netfilter module allows revision 0 rules to reuse timers created by revision 1 rules, but when those timers use ALARM type semantics (a special timer mode), the underlying timer structure is never initialized. This causes a crash when revision 0 tries to modify the uninitialized timer. The fix rejects revision 0 rules from reusing ALARM-type timers with the same label.