{"id":"CVE-2026-46319","title":"net/sched: act_ct: Only release RCU read lock after ct_ft","summary":"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 …","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < ece578ca61e572df96cfc80456357ebfae0b4b9e","Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < a2e0c045c87aa252eb61412e67dd91f2c2b19f81","Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < 67c9ecc9f2575273ed1323e312881fc98ac83d6d","Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < f23424a0ddadb494d4bd57056a7ca703312d3a7b","Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < 17dfb67cb399b660105d9a8c6100851c0d0cdc70","Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < 4c727c6967a41b37efe0f26332ca9ec5b74785a3","Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < 3e20e1b3058e0b94638e7b931c138e840e266724","Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < f462dca0c8415bf0058d0ffa476354c4476d0f09","Linux 5.7"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-10-16T15:21:58.359342Z"},"published":"2026-06-09","updated":"2026-10-16","sourceUpdated":"2026-10-16T15:31:16.462Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-46319","references":[{"url":"https://git.kernel.org/stable/c/ece578ca61e572df96cfc80456357ebfae0b4b9e"},{"url":"https://git.kernel.org/stable/c/a2e0c045c87aa252eb61412e67dd91f2c2b19f81"},{"url":"https://git.kernel.org/stable/c/67c9ecc9f2575273ed1323e312881fc98ac83d6d"},{"url":"https://git.kernel.org/stable/c/f23424a0ddadb494d4bd57056a7ca703312d3a7b"},{"url":"https://git.kernel.org/stable/c/17dfb67cb399b660105d9a8c6100851c0d0cdc70"},{"url":"https://git.kernel.org/stable/c/4c727c6967a41b37efe0f26332ca9ec5b74785a3"},{"url":"https://git.kernel.org/stable/c/3e20e1b3058e0b94638e7b931c138e840e266724"},{"url":"https://git.kernel.org/stable/c/f462dca0c8415bf0058d0ffa476354c4476d0f09"}],"tags":["cve.org"],"epss":0.00132,"epssPercentile":0.02439,"ingestedAt":"2026-10-16T17:24:46.716Z","slug":"CVE-2026-46319","body":"## Overview\n\nIn 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->zone };\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->ref)) // [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->ref) 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->ref)) {\n                                rhashtable_remove_fast(&zones_ht, &ct_ft->node, zones_params);\n                                INIT_RCU_WORK(&ct_ft->rwork, tcf_ct_flow_table_cleanup_work); // [3]\n                                queue_rcu_work(act_ct_wq, &ct_ft->rwork);\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->nf_ft);\n                block = &ct_ft->nf_ft.flow_block;\n                down_write(&ct_ft->nf_ft.flow_block_lock);\n                WARN_ON(!list_empty(&block->cb_list));\n                up_write(&ct_ft->nf_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]\n\n## Affected\n\n- `Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < ece578ca61e572df96cfc80456357ebfae0b4b9e`\n- `Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < a2e0c045c87aa252eb61412e67dd91f2c2b19f81`\n- `Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < 67c9ecc9f2575273ed1323e312881fc98ac83d6d`\n- `Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < f23424a0ddadb494d4bd57056a7ca703312d3a7b`\n- `Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < 17dfb67cb399b660105d9a8c6100851c0d0cdc70`\n- `Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < 4c727c6967a41b37efe0f26332ca9ec5b74785a3`\n- `Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < 3e20e1b3058e0b94638e7b931c138e840e266724`\n- `Linux >= 138470a9b2cc2e26e6018300394afc3858a54e6a < f462dca0c8415bf0058d0ffa476354c4476d0f09`\n- `Linux 5.7`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}