{
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
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"cveId": "CVE-2024-41040",
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"state": "PUBLISHED",
"assignerShortName": "Linux",
"dateReserved": "2024-07-12T12:17:45.621Z",
"datePublished": "2024-07-29T14:31:53.853Z",
"dateUpdated": "2026-08-05T11:34:54.957Z"
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Fix UAF when resolving a clash\n\nKASAN reports the following UAF:\n\n BUG: KASAN: slab-use-after-free in tcf_ct_flow_table_process_conn+0x12b/0x380 [act_ct]\n Read of size 1 at addr ffff888c07603600 by task handler130/6469\n\n Call Trace:\n \n dump_stack_lvl+0x48/0x70\n print_address_description.constprop.0+0x33/0x3d0\n print_report+0xc0/0x2b0\n kasan_report+0xd0/0x120\n __asan_load1+0x6c/0x80\n tcf_ct_flow_table_process_conn+0x12b/0x380 [act_ct]\n tcf_ct_act+0x886/0x1350 [act_ct]\n tcf_action_exec+0xf8/0x1f0\n fl_classify+0x355/0x360 [cls_flower]\n __tcf_classify+0x1fd/0x330\n tcf_classify+0x21c/0x3c0\n sch_handle_ingress.constprop.0+0x2c5/0x500\n __netif_receive_skb_core.constprop.0+0xb25/0x1510\n __netif_receive_skb_list_core+0x220/0x4c0\n netif_receive_skb_list_internal+0x446/0x620\n napi_complete_done+0x157/0x3d0\n gro_cell_poll+0xcf/0x100\n __napi_poll+0x65/0x310\n net_rx_action+0x30c/0x5c0\n __do_softirq+0x14f/0x491\n __irq_exit_rcu+0x82/0xc0\n irq_exit_rcu+0xe/0x20\n common_interrupt+0xa1/0xb0\n \n \n asm_common_interrupt+0x27/0x40\n\n Allocated by task 6469:\n kasan_save_stack+0x38/0x70\n kasan_set_track+0x25/0x40\n kasan_save_alloc_info+0x1e/0x40\n __kasan_krealloc+0x133/0x190\n krealloc+0xaa/0x130\n nf_ct_ext_add+0xed/0x230 [nf_conntrack]\n tcf_ct_act+0x1095/0x1350 [act_ct]\n tcf_action_exec+0xf8/0x1f0\n fl_classify+0x355/0x360 [cls_flower]\n __tcf_classify+0x1fd/0x330\n tcf_classify+0x21c/0x3c0\n sch_handle_ingress.constprop.0+0x2c5/0x500\n __netif_receive_skb_core.constprop.0+0xb25/0x1510\n __netif_receive_skb_list_core+0x220/0x4c0\n netif_receive_skb_list_internal+0x446/0x620\n napi_complete_done+0x157/0x3d0\n gro_cell_poll+0xcf/0x100\n __napi_poll+0x65/0x310\n net_rx_action+0x30c/0x5c0\n __do_softirq+0x14f/0x491\n\n Freed by task 6469:\n kasan_save_stack+0x38/0x70\n kasan_set_track+0x25/0x40\n kasan_save_free_info+0x2b/0x60\n ____kasan_slab_free+0x180/0x1f0\n __kasan_slab_free+0x12/0x30\n slab_free_freelist_hook+0xd2/0x1a0\n __kmem_cache_free+0x1a2/0x2f0\n kfree+0x78/0x120\n nf_conntrack_free+0x74/0x130 [nf_conntrack]\n nf_ct_destroy+0xb2/0x140 [nf_conntrack]\n __nf_ct_resolve_clash+0x529/0x5d0 [nf_conntrack]\n nf_ct_resolve_clash+0xf6/0x490 [nf_conntrack]\n __nf_conntrack_confirm+0x2c6/0x770 [nf_conntrack]\n tcf_ct_act+0x12ad/0x1350 [act_ct]\n tcf_action_exec+0xf8/0x1f0\n fl_classify+0x355/0x360 [cls_flower]\n __tcf_classify+0x1fd/0x330\n tcf_classify+0x21c/0x3c0\n sch_handle_ingress.constprop.0+0x2c5/0x500\n __netif_receive_skb_core.constprop.0+0xb25/0x1510\n __netif_receive_skb_list_core+0x220/0x4c0\n netif_receive_skb_list_internal+0x446/0x620\n napi_complete_done+0x157/0x3d0\n gro_cell_poll+0xcf/0x100\n __napi_poll+0x65/0x310\n net_rx_action+0x30c/0x5c0\n __do_softirq+0x14f/0x491\n\nThe ct may be dropped if a clash has been resolved but is still passed to\nthe tcf_ct_flow_table_process_conn function for further usage. This issue\ncan be fixed by retrieving ct from skb again after confirming conntrack."
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"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
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"value": "AV:N - The vulnerable code executes in the NAPI receive softirq (`sch_handle_ingress` → `tcf_classify` → `tcf_ct_act`) on data taken directly from arriving packets, as the KASAN ``/`net_rx_action` trace shows. On any host configured with `action ct commit` (OVS-TC/OVN/Kubernetes offload nodes, the subsystem's primary deployment), an off-host attacker triggers it purely by sending routable UDP/ICMP/GRE traffic to or through the node.\nAC:L - The attacker controls both sides of the race by flooding packets with an identical 5-tuple, which RSS spreads across CPUs so two unconfirmed conntracks reach `nf_conntrack_confirm` concurrently — conntrack clashes on UDP bursts are so routine that the kernel has dedicated clash-resolution machinery and counters for them. Once a clash occurs the free of the loser ct and the subsequent stale dereference are deterministic.\nPR:N - Conntrack processing happens on ingress before any application-layer authentication or socket delivery, so the attacker needs no account, credentials, or local access on the target. The tc/act_ct configuration is established by the administrator as part of normal deployment, not by the attacker.\nUI:N - The UAF is triggered entirely by unsolicited inbound packets processed in softirq context; no local user or administrator has to open, mount, or interact with anything.\nS:U - The freed conntrack object, the corrupting writes, and the impacted flow-offload table all live within the same host kernel's security authority. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - The freed `nf_ct_ext` is a plain kmalloc object that an attacker can reclaim and spray, and `nf_conn_act_ct_ext_find()` uses an attacker-controlled `u8` offset from it as a pointer offset, yielding a controlled out-of-bounds read whose result is written into the offload tuple. The dangling `nf_conn` is also read wholesale into the flow entry, exposing reclaimed kernel memory.\nI:H - `tcf_ct_flow_table_add()` writes into the freed object — `test_and_set_bit(IPS_OFFLOAD_BIT, &ct->status)`, `refcount_inc(&ct->ct_general.use)`, and `ct->proto.tcp.seen[].flags |=` — and persists `flow->ct` as a dangling pointer in the flow-offload table. With the `nf_conn` slab (SLAB_TYPESAFE_BY_RCU) reclaimed by attacker-sprayed connections, this produces refcount confusion and later double-free/UAF on a live object, a classic path to control-flow hijack.\nA:H - The use-after-free reliably crashes the kernel in softirq context under KASAN or slab poisoning, and unpoisoned it corrupts conntrack refcounting and the flow-offload table, leading to oops or panic. The attacker can repeat the packet flood indefinitely to keep re-triggering it."
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