UBUNTU-CVE-2026-97609: Use After Free

In the Linux kernel, the following vulnerability has been resolved: netfilter: cttimeout: prevent UAF during module unload nfctsettimeout() protects the timeout hook dereference and policy lookup with rcureadlock(). cttimeoutexit(), however, unregisters the per-net operations before it clears the hook. This allows the following interleaving: CPU 0 CPU 1 cttimeoutexit() nfctsettimeout() unregisterpernetsubsys() rcureadlock() kfree(pernet) h = nfcttimeouthook h->timeoutfindget() nfcttimeoutpernet() The hook still points to ctnltimeoutfindget() when CPU 1 looks up the already freed per-net timeout list. KASAN reported: BUG: KASAN: slab-use-after-free in ctnltimeoutfindget Read of size 8 by task poc/90 Call Trace: ctnltimeoutfindget+0x271/0x2a0 [nfnetlinkcttimeout] nfctsettimeout+0x7b/0x3c0 xtcttgcheck+0x724/0xb20 xtchecktarget+0x234/0xa90 doiptsetctl+0x570/0x1270 Allocated by task 89: kmallocnoprof+0x16e/0x460 opsinit+0x6d/0x420 registerpernetoperations+0x2f6/0x670 Freed by task 91: kfree+0x131/0x390 opsundolist+0x3d4/0x730 unregisterpernetoperations+0x232/0x490 unregisterpernetsubsys+0x1c/0x30 cttimeoutexit+0x52/0x970 [nfnetlinkcttimeout] Clear the hook and wait for existing readers before unregistering the per-net operations. This blocks new policy lookups and ensures readers that observed the hook finish before the per-net storage is freed.