CVE-2026-72123 (GCVE-0-2026-72123)
Vulnerability from cvelistv5
Published
2026-08-15 05:53
Modified
2026-08-19 16:36
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF
Commit f1b4e32aca08 ("can: bcm: use call_rcu() instead of costly
synchronize_rcu()") replaced synchronize_rcu() in bcm_delete_rx_op()
with call_rcu() and introduced the RX_NO_AUTOTIMER flag.
However, this flag check was omitted for thrtimer in the packet rx
fast-path. During BCM RX operation teardown, a concurrent RCU reader
(bcm_rx_handler) can race and re-arm thrtimer via
bcm_rx_update_and_send() after call_rcu() has been scheduled. Once
the RCU grace period elapses, bcm_op is freed. The subsequently
firing thrtimer then dereferences the deallocated op, causing a UAF.
Adding flag checks to the rx fast-path (bcm_rx_update_and_send) does not
fully close the TOCTOU race and introduces latency for every CAN frame.
Conversely, calling hrtimer_cancel() directly inside the RCU callback
(softirq context) is fatal as hrtimer_cancel() can sleep, triggering
a "scheduling while atomic" panic.
Resolve this by deferring the timer cancellation and memory free to a
dedicated unbound workqueue (bcm_wq). The RCU callback now queues a
work item to bcm_wq, which safely cancels both timers and deallocates
memory in sleepable process context. A dedicated workqueue is used to
prevent system-wide WQ saturation and is cleanly flushed/destroyed
on module unload to avoid rmmod page faults.
Since the deferred work can now outlive the calling context by an
unbounded amount, also take a reference on op->sk when it is assigned
and drop it only once the deferred work has cancelled both timers, so a
socket can no longer be freed out from under a still-armed timer whose
callback (bcm_send_to_user()) dereferences op->sk.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: 85cd41070df992d3c0dfd828866fdd243d3b774a Version: f34f2a18e47b73e48f90a757e1f4aaa8c7d665a1 Version: f1b4e32aca0811aa011c76e5d6cf2fa19224b386 Version: f1b4e32aca0811aa011c76e5d6cf2fa19224b386 Version: f1b4e32aca0811aa011c76e5d6cf2fa19224b386 Version: f1b4e32aca0811aa011c76e5d6cf2fa19224b386 Version: f1b4e32aca0811aa011c76e5d6cf2fa19224b386 Version: f1b4e32aca0811aa011c76e5d6cf2fa19224b386 Version: fbac09a3b8890003c0c55294c00709f3ae5501bb Version: 5b48f5711f1c630841ab78dcc061de902f0e37bf Version: edb4baffb9483141a50fb7f7146cfe4a4c0c2db8 Version: 5.10.130 ≤ Version: 5.15.54 ≤ Version: 4.19.252 ≤ Version: 5.4.205 ≤ Version: 5.18.11 ≤ |
||
{
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},
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"status": "affected",
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},
{
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{
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],
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"vendor": "Linux",
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{
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},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.145",
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},
{
"lessThanOrEqual": "6.12.*",
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},
{
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{
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"version": "7.1.5",
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},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
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],
"negate": false,
"operator": "OR"
}
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],
"descriptions": [
{
"lang": "en",
"value": "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 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-\u003esk 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-\u003esk."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - Exploitation requires local BCM socket syscalls (sendmsg with RX_SETUP/SETTIMER/ival2 throttling and RX_DELETE); CAN frames can be injected locally via loopback without physical bus access.\nAC:L - The attacker controls both sides of the race by concurrently issuing RX_DELETE teardown and delivering matching CAN frames (e.g., via threads or paired BCM/RAW sockets), making the thrtimer re-arm UAF reliably triggerable.\nPR:L - No kernel capability check gates AF_CAN/CAN_BCM socket creation or bcm_sendmsg opcodes; any unprivileged local user with socket access (including via user namespaces with vcan) can reach the vulnerable path.\nUI:N - No victim interaction is required; the attacker self-triggers the race through their own BCM socket operations and locally injected CAN traffic.\nS:U - Impact is confined to kernel memory corruption and local privilege escalation within the same kernel security boundary, not a cross-boundary escape such as VM or IOMMU bypass.\nC:H - The thrtimer UAF dereferences freed bcm_op fields (locks, frame buffers, op-\u003esk) in bcm_rx_thr_handler/bcm_send_to_user, enabling attacker-controlled heap reuse and arbitrary kernel memory disclosure.\nI:H - UAF on the bcm_op slab object allows heap spraying to corrupt function pointers, timers, and sock structures, providing a standard path to arbitrary kernel writes and local privilege escalation.\nA:H - The freed-op dereference in the hrtimer softirq path causes kernel oops/panic under normal exploitation attempts, and successful memory corruption can crash or hang the system."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-19T16:36:18.988Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"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"
}
],
"title": "can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-72123",
"datePublished": "2026-08-15T05:53:01.433Z",
"dateReserved": "2026-08-09T03:40:39.907Z",
"dateUpdated": "2026-08-19T16:36:18.988Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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