{"id":"AZL-89681","summary":"CVE-2026-46319 affecting package kernel for versions less than 6.6.141.1-1","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: act_ct: Only release RCU read lock after ct_ft\n\nWhen looking up a flow table in act_ct in tcf_ct_flow_table_get(),\nrhashtable_lookup_fast() internally opens and closes an RCU read critical\nsection before returning ct_ft.\nThe tcf_ct_flow_table_cleanup_work() can complete before refcount_inc_not_zero()\nis invoked on the returned ct_ft resulting in a UAF on the already freed ct_ft\nobject. This vulnerability can lead to privilege escalation.\n\nAnalysis from zdi-disclosures@trendmicro.com:\nWhen initializing act_ct, tcf_ct_init() is called, which internally triggers\ntcf_ct_flow_table_get().\n\nstatic int tcf_ct_flow_table_get(struct net *net, struct tcf_ct_params *params)\n\n{\n                struct zones_ht_key key = { .net = net, .zone = params-\u003ezone };\n                struct tcf_ct_flow_table *ct_ft;\n                int err = -ENOMEM;\n\n                mutex_lock(&zones_mutex);\n                ct_ft = rhashtable_lookup_fast(&zones_ht, &key, zones_params); // [1]\n                if (ct_ft && refcount_inc_not_zero(&ct_ft-\u003eref)) // [2]\n                                goto out_unlock;\n                ...\n}\n\nstatic __always_inline void *rhashtable_lookup_fast(\n                struct rhashtable *ht, const void *key,\n                const struct rhashtable_params params)\n{\n                void *obj;\n\n                rcu_read_lock();\n                obj = rhashtable_lookup(ht, key, params);\n                rcu_read_unlock();\n\n                return obj;\n}\n\nAt [1], rhashtable_lookup_fast() looks up and returns the corresponding ct_ft\nfrom zones_ht . The lookup is performed within an RCU read critical section\nthrough rcu_read_lock() / rcu_read_unlock(), which prevents the object from\nbeing freed. However, at the point of function return, rcu_read_unlock() has\nalready been called, and there is nothing preventing ct_ft from being freed\nbefore reaching refcount_inc_not_zero(&ct_ft-\u003eref) at [2]. This interval becomes\nthe race window, during which ct_ft can be freed.\n\nFree Process:\n\ntcf_ct_flow_table_put() is executed through the path tcf_ct_cleanup() call_rcu()\ntcf_ct_params_free_rcu() tcf_ct_params_free() tcf_ct_flow_table_put().\n\nstatic void tcf_ct_flow_table_put(struct tcf_ct_flow_table *ct_ft)\n{\n                if (refcount_dec_and_test(&ct_ft-\u003eref)) {\n                                rhashtable_remove_fast(&zones_ht, &ct_ft-\u003enode, zones_params);\n                                INIT_RCU_WORK(&ct_ft-\u003erwork, tcf_ct_flow_table_cleanup_work); // [3]\n                                queue_rcu_work(act_ct_wq, &ct_ft-\u003erwork);\n                }\n}\n\nAt [3], tcf_ct_flow_table_cleanup_work() is scheduled as RCU work\n\nstatic void tcf_ct_flow_table_cleanup_work(struct work_struct *work)\n\n{\n                struct tcf_ct_flow_table *ct_ft;\n                struct flow_block *block;\n\n                ct_ft = container_of(to_rcu_work(work), struct tcf_ct_flow_table,\n                                                                rwork);\n                nf_flow_table_free(&ct_ft-\u003enf_ft);\n                block = &ct_ft-\u003enf_ft.flow_block;\n                down_write(&ct_ft-\u003enf_ft.flow_block_lock);\n                WARN_ON(!list_empty(&block-\u003ecb_list));\n                up_write(&ct_ft-\u003enf_ft.flow_block_lock);\n                kfree(ct_ft); // [4]\n\n                module_put(THIS_MODULE);\n}\n\ntcf_ct_flow_table_cleanup_work() frees ct_ft at [4]. When this function executes\nbetween [1] and [2], UAF occurs.\n\nThis race condition has a very short race window, making it generally\ndifficult to trigger. Therefore, to trigger the vulnerability an msleep(100) was\ninserted after[1]","modified":"2026-08-28T17:47:35.111996850Z","published":"2026-06-09T13:16:37Z","upstream":["CVE-2026-46319"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-46319"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6.141.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-89681.json"}}],"schema_version":"1.9.0"}