{"id":"CVE-2026-72123","title":"can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\ncan: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF\n\nCommit f1b4e32aca08 (\"can: bcm: use call_rcu() instead of costly\nsynchronize_rcu()\") replaced synch…","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 >= 85cd41070df992d3c0dfd828866fdd243d3b774a < de5fce46637de05bef56ec08528127676eb6fc9b","Linux >= f34f2a18e47b73e48f90a757e1f4aaa8c7d665a1 < 036a8c320ca11bc912e8027adcfad14b326f067e","Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 3cf4fd5316f449811d8baf1bc6978ef5a7b743a9","Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 4177762f70646ac48a2af382e45a795cbd295198","Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 6fd08e8d826c3aa4cc7021f5f9cdbb7fa7441d3f","Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < cd830e0bc25ee2d38cbfbdbb3cd77c5f53b2b6d5","Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < ce2d4b121fb7545e1ed588e860c8e5fd5ad45224","Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 68973f9db76144825e4f35dfdc80fb8279eb2d57","Linux fbac09a3b8890003c0c55294c00709f3ae5501bb","Linux 5b48f5711f1c630841ab78dcc061de902f0e37bf","Linux edb4baffb9483141a50fb7f7146cfe4a4c0c2db8","Linux >= 5.10.130 < 5.10.265","Linux >= 5.15.54 < 5.15.216","Linux >= 4.19.252 < 4.20","Linux >= 5.4.205 < 5.5","Linux >= 5.18.11 < 5.19","Linux 5.19"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-10-16T18:42:12.952847Z"},"published":"2026-08-15","updated":"2026-10-16","sourceUpdated":"2026-10-16T18:44:57.598Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-72123","references":[{"url":"https://git.kernel.org/stable/c/de5fce46637de05bef56ec08528127676eb6fc9b"},{"url":"https://git.kernel.org/stable/c/036a8c320ca11bc912e8027adcfad14b326f067e"},{"url":"https://git.kernel.org/stable/c/3cf4fd5316f449811d8baf1bc6978ef5a7b743a9"},{"url":"https://git.kernel.org/stable/c/4177762f70646ac48a2af382e45a795cbd295198"},{"url":"https://git.kernel.org/stable/c/6fd08e8d826c3aa4cc7021f5f9cdbb7fa7441d3f"},{"url":"https://git.kernel.org/stable/c/cd830e0bc25ee2d38cbfbdbb3cd77c5f53b2b6d5"},{"url":"https://git.kernel.org/stable/c/ce2d4b121fb7545e1ed588e860c8e5fd5ad45224"},{"url":"https://git.kernel.org/stable/c/68973f9db76144825e4f35dfdc80fb8279eb2d57"}],"tags":["cve.org"],"epss":0.00169,"epssPercentile":0.05786,"ingestedAt":"2026-10-16T19:46:24.431Z","slug":"CVE-2026-72123","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\ncan: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF\n\nCommit f1b4e32aca08 (\"can: bcm: use call_rcu() instead of costly\nsynchronize_rcu()\") replaced synchronize_rcu() in bcm_delete_rx_op()\nwith call_rcu() and introduced the RX_NO_AUTOTIMER flag.\n\nHowever, this flag check was omitted for thrtimer in the packet rx\nfast-path. During BCM RX operation teardown, a concurrent RCU reader\n(bcm_rx_handler) can race and re-arm thrtimer via\nbcm_rx_update_and_send() after call_rcu() has been scheduled.  Once\nthe RCU grace period elapses, bcm_op is freed.  The subsequently\nfiring thrtimer then dereferences the deallocated op, causing a UAF.\n\nAdding flag checks to the rx fast-path (bcm_rx_update_and_send) does not\nfully close the TOCTOU race and introduces latency for every CAN frame.\nConversely, calling hrtimer_cancel() directly inside the RCU callback\n(softirq context) is fatal as hrtimer_cancel() can sleep, triggering\na \"scheduling while atomic\" panic.\n\nResolve this by deferring the timer cancellation and memory free to a\ndedicated unbound workqueue (bcm_wq).  The RCU callback now queues a\nwork item to bcm_wq, which safely cancels both timers and deallocates\nmemory in sleepable process context.  A dedicated workqueue is used to\nprevent system-wide WQ saturation and is cleanly flushed/destroyed\non module unload to avoid rmmod page faults.\n\nSince the deferred work can now outlive the calling context by an\nunbounded amount, also take a reference on op->sk when it is assigned\nand drop it only once the deferred work has cancelled both timers, so a\nsocket can no longer be freed out from under a still-armed timer whose\ncallback (bcm_send_to_user()) dereferences op->sk.\n\n## Affected\n\n- `Linux >= 85cd41070df992d3c0dfd828866fdd243d3b774a < de5fce46637de05bef56ec08528127676eb6fc9b`\n- `Linux >= f34f2a18e47b73e48f90a757e1f4aaa8c7d665a1 < 036a8c320ca11bc912e8027adcfad14b326f067e`\n- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 3cf4fd5316f449811d8baf1bc6978ef5a7b743a9`\n- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 4177762f70646ac48a2af382e45a795cbd295198`\n- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 6fd08e8d826c3aa4cc7021f5f9cdbb7fa7441d3f`\n- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < cd830e0bc25ee2d38cbfbdbb3cd77c5f53b2b6d5`\n- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < ce2d4b121fb7545e1ed588e860c8e5fd5ad45224`\n- `Linux >= f1b4e32aca0811aa011c76e5d6cf2fa19224b386 < 68973f9db76144825e4f35dfdc80fb8279eb2d57`\n- `Linux fbac09a3b8890003c0c55294c00709f3ae5501bb`\n- `Linux 5b48f5711f1c630841ab78dcc061de902f0e37bf`\n- `Linux edb4baffb9483141a50fb7f7146cfe4a4c0c2db8`\n- `Linux >= 5.10.130 < 5.10.265`\n- `Linux >= 5.15.54 < 5.15.216`\n- `Linux >= 4.19.252 < 4.20`\n- `Linux >= 5.4.205 < 5.5`\n- `Linux >= 5.18.11 < 5.19`\n- `Linux 5.19`\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":[]}