UBUNTU-CVE-2026-72126: Use After Free
In the Linux kernel, the following vulnerability has been resolved: can: isotp: use unconditional synchronizercu() in isotprelease() isotpnotify() unregisters the (RCU) CAN filters via canrxunregister() and clears so->bound without waiting for a grace period. isotprelease() uses so->bound to decide whether it needs to call synchronizercu() before cancelling so->rxtimer, so when NETDEVUNREGISTER runs first it skips that synchronizercu() and can cancel the timer while an in-flight isotprcv() is still executing and about to re-arm it via isotpsendfc(), leading to a use-after-free timer callback on the freed socket. sakisho-bot remarked a problem with rtnllock held in isotpnotify(), therefore make isotprelease() always call synchronizercu() before cancelling the timers, regardless of so->bound. This still closes the original race (isotpnotify() clearing so->bound without waiting for in-flight isotprcv() callers before isotprelease() cancels the RX timer) without adding any RCU wait to the netdevice notifier path.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 6.8.1-1062.63 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1067.70+fips1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79+fips1 - Upgrade
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-147.147+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79+fips1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-38.38 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1016.16 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 7.0.0-1008.9 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1015.15 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1015.15 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1013.13 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Compensating control
Update isotp_release() to unconditionally call synchronize_rcu() before cancelling the timers, regardless of so->bound.
Event History
Frequently Asked Questions
What conditions are needed to trigger the race?
An ISO-TP receive handler must still be in flight while the associated CAN netdevice is being unregistered and the socket is released. The receive handler can then re-arm the receive timer after release has cancelled it, resulting in a timer callback on a freed socket.
Why does netdevice unregistration matter?
The netdevice notifier unregisters the RCU CAN filters and clears the socket's bound state without waiting for an RCU grace period. Previously, that cleared bound state could cause socket release to skip the synchronization needed before cancelling timers.
What is the relevant remediation behavior?
The fix makes socket release call synchronize_rcu() unconditionally before cancelling the timers, rather than basing that decision on whether the socket is still marked as bound. This waits for in-flight ISO-TP receive handlers without adding an RCU wait to the netdevice notifier path.