{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-74289", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-08-15T05:44:03.881Z", "datePublished": "2026-08-15T05:57:56.383Z", "dateUpdated": "2026-08-17T05:45:28.941Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-17T05:45:28.941Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: fib: Don't dump dying fib_info in fib_leaf_notify().\n\nsyzbot reported use-after-free in nsim_fib4_prepare_event(). [0]\n\nThe problem is that the following functions call fib_info_hold() /\nrefcount_inc() while dumping fib_info under RCU, which is unsafe.\n\n * mlxsw_sp_router_fib4_event()\n * rocker_router_fib_event()\n * nsim_fib4_prepare_event()\n\nrefcount_inc_not_zero() must be used, but it would be too late\nthere.\n\nLet's guarantee the lifetime of fib_info in fib_leaf_notify().\n\nNote that IPv6 does not need the corresponding change since\nfib6_table_dump() holds fib6_table.tb6_lock.\n\n[0]:\nrefcount_t: addition on 0; use-after-free.\nWARNING: lib/refcount.c:25 at refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25, CPU#0: kworker/u8:15/3420\nModules linked in:\nCPU: 0 UID: 0 PID: 3420 Comm: kworker/u8:15 Not tainted syzkaller #0 PREEMPT_{RT,(full)}\nHardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026\nWorkqueue: netns cleanup_net\nRIP: 0010:refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25\nCode: eb 66 85 db 74 3e 83 fb 01 75 4c e8 1b f1 22 fd 48 8d 3d 84 cb f1 0a 67 48 0f b9 3a eb 4a e8 08 f1 22 fd 48 8d 3d 81 cb f1 0a <67> 48 0f b9 3a eb 37 e8 f5 f0 22 fd 48 8d 3d 7e cb f1 0a 67 48 0f\nRSP: 0018:ffffc9000f2c7270 EFLAGS: 00010293\nRAX: ffffffff84a18858 RBX: 0000000000000002 RCX: ffff888032ff9ec0\nRDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8f9353e0\nRBP: 0000000000000000 R08: ffff888032ff9ec0 R09: 0000000000000005\nR10: 0000000000000100 R11: 0000000000000004 R12: ffff8880570cc000\nR13: dffffc0000000000 R14: ffff88802b40563c R15: ffff8880570cc000\nFS: 0000000000000000(0000) GS:ffff888126173000(0000) knlGS:0000000000000000\nCS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 00007fb1f4d5d000 CR3: 000000006072a000 CR4: 00000000003526f0\nCall Trace:\n \n __refcount_add include/linux/refcount.h:-1 [inline]\n __refcount_inc include/linux/refcount.h:366 [inline]\n refcount_inc include/linux/refcount.h:383 [inline]\n fib_info_hold include/net/ip_fib.h:629 [inline]\n nsim_fib4_prepare_event drivers/net/netdevsim/fib.c:930 [inline]\n nsim_fib_event_schedule_work drivers/net/netdevsim/fib.c:1000 [inline]\n nsim_fib_event_nb+0x1055/0x1240 drivers/net/netdevsim/fib.c:1043\n call_fib_notifier+0x45/0x80 net/core/fib_notifier.c:25\n call_fib_entry_notifier net/ipv4/fib_trie.c:90 [inline]\n fib_leaf_notify net/ipv4/fib_trie.c:2176 [inline]\n fib_table_notify net/ipv4/fib_trie.c:2194 [inline]\n fib_notify+0x36b/0x5e0 net/ipv4/fib_trie.c:2217\n fib_net_dump net/core/fib_notifier.c:70 [inline]\n register_fib_notifier+0x184/0x360 net/core/fib_notifier.c:108\n nsim_fib_create+0x85d/0x9f0 drivers/net/netdevsim/fib.c:1596\n nsim_dev_reload_create drivers/net/netdevsim/dev.c:1604 [inline]\n nsim_dev_reload_up+0x374/0x7c0 drivers/net/netdevsim/dev.c:1058\n devlink_reload+0x501/0x8d0 net/devlink/dev.c:475\n devlink_pernet_pre_exit+0x1ff/0x420 net/devlink/core.c:558\n ops_pre_exit_list net/core/net_namespace.c:161 [inline]\n ops_undo_list+0x187/0x940 net/core/net_namespace.c:234\n cleanup_net+0x56e/0x800 net/core/net_namespace.c:702\n process_one_work kernel/workqueue.c:3314 [inline]\n process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3397\n worker_thread+0xa53/0xfc0 kernel/workqueue.c:3478\n kthread+0x388/0x470 kernel/kthread.c:436\n ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158\n ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245\n " } ], "metrics": [ { "cvssV3_1": { "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" }, "scenarios": [ { "lang": "en", "value": "AV:L - Exploitation requires local netlink syscalls (rtnetlink route add/delete and devlink reload/netns teardown) that invoke register_fib_notifier()->fib_leaf_notify(); it is not reachable by sending remote IP packets.\nAC:L - The bug is a race between RCU FIB table dump and concurrent route deletion; an attacker controls both sides by churning routes while triggering devlink reload or network-namespace cleanup that registers a FIB notifier.\nPR:L - Route manipulation and devlink operations require CAP_NET_ADMIN in the target network namespace, which an unprivileged local user can obtain via user+network namespaces; cloud/container hosts with Mellanox mlx5/mlxsw also expose this via NET_ADMIN.\nUI:N - No victim interaction is required; the attacker creates routes, triggers FIB notifier registration/dump, and concurrently deletes routes or destroys the namespace themselves.\nS:U - Impact is a kernel heap use-after-free within the host networking stack; it does not cross VM, container, or IOMMU security boundaries (standard kernel privilege escalation remains scope Unchanged).\nC:H - Use-after-free on fib_info during RCU dump (refcount_inc on zero in fib_info_hold); syzbot confirmed dying fib_info access, enabling disclosure of freed slab contents and kernel pointer leaks for further exploitation.\nI:H - UAF on fib_info allows attacker-controlled heap reuse of the freed object, enabling arbitrary kernel memory corruption, control-flow hijack, and local privilege escalation beyond the demonstrated refcount warning.\nA:H - Demonstrated kernel refcount UAF warning/crash path during fib_info_hold; repeated triggering via route churn plus devlink reload/netns cleanup can panic or hang the host, causing system-wide denial of service." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "include/net/ip_fib.h", "net/ipv4/fib_trie.c" ], "versions": [ { "version": "c3852ef7f2f8f75a9f85a864bec1f6f5a3068eea", "lessThan": "676482da8d938ea72c26da0fc86af2d2ec238ab2", "status": "affected", "versionType": "git" }, { "version": "c3852ef7f2f8f75a9f85a864bec1f6f5a3068eea", "lessThan": "06b693d2eb6651a63ad85bad8673de3b7d4edd6d", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "include/net/ip_fib.h", "net/ipv4/fib_trie.c" ], "versions": [ { "version": "4.10", "status": "affected" }, { "version": "0", "lessThan": "4.10", "status": "unaffected", "versionType": "semver" }, { "version": "7.1.5", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.10", "versionEndExcluding": "7.1.5" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.10", "versionEndExcluding": "7.2" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/676482da8d938ea72c26da0fc86af2d2ec238ab2" }, { "url": "https://git.kernel.org/stable/c/06b693d2eb6651a63ad85bad8673de3b7d4edd6d" } ], "title": "ipv4: fib: Don't dump dying fib_info in fib_leaf_notify().", "x_generator": { "engine": "bippy-1.2.0" } } } }