UBUNTU-CVE-2026-63990: Medium severity ubuntu/linux vulnerability
In the Linux kernel, the following vulnerability has been resolved: bonding: refuse to enslave CAN devices syzbot reported a kernel paging request crash in canrxunregister() inside net/can/afcan.c. The crash occurs because a virtual CAN device (vxcan) is being enslaved to a bonding master. During the enslavement process, the bonding driver mutates and modifies the network device states to fit an Ethernet-like aggregation model. However, CAN devices operate on a completely different Layer 2 architecture, relying on the CAN mid-layer private data structure (canmlpriv) instead of standard Ethernet structures. Since bonding does not initialize or maintain these CAN structures, subsequent operations on the half-enslaved interface (such as closing associated sockets via isotprelease) lead to a null-pointer dereference when accessing the CAN receiver lists. Bonding CAN interfaces is architecturally invalid as CAN lacks MAC addresses, ARP capabilities, and standard Ethernet link-layer mechanisms. While generic loopback devices are blocked globally in net/core/dev.c, virtual CAN devices bypass this check because they do not carry the IFFLOOPBACK flag, despite acting as local software-loopbacks. Fix this by explicitly blocking network devices of type ARPHRDCAN from being enslaved at the very beginning of bondenslave(). This prevents illegal state mutations, eliminates the resulting KASAN crashes, and avoids potential memory leaks from incomplete socket cleanups. As the CAN support has been added a long time after bonding the Fixes-tag points to the introduction of ARPHRDCAN that would have needed a specific handling in bondingmain.c.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1117.124~20.04.1 - Upgrade
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ubuntu/linux-gcp-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1011.11~24.04.1 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-28.28~24.04.1 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 6.8.0-1066.67 - Upgrade
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ubuntu/linux-lowlatencyto a version that resolves this vulnerability.Fixed in 6.8.0-146.146.1 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 6.8.0-1064.67 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1070.78+fips1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-28.28 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1009.9 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1010.10 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1008.8 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 7.0.0-1003.4 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1010.10 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 7.0.0-1016.16 - Upgrade
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ubuntu/linux-nvidia-bosto a version that resolves this vulnerability.Fixed in 7.0.0-2016.16 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1009.9 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1008.8 - Upgrade
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ubuntu/linux-raspito a version that resolves this vulnerability.Fixed in 7.0.0-1015.15 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 7.0.0-28.28.1 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-28.28.1 - Compensating control
Modify the bonding driver so bond_enslave() explicitly rejects network devices of type ARPHRD_CAN before any device-state mutation or enslavement occurs.
Event History
Frequently Asked Questions
Who is realistically exposed to this issue?
Systems are exposed if a local user with sufficient network configuration privileges can enslave a virtual CAN (vxcan) device to a bonding master. The listed affected Ubuntu kernel packages include standard, cloud, and FIPS kernel variants.
What does an attacker need to trigger the crash?
The attacker needs local access and low-complexity ability to configure network interfaces, specifically to add a vxcan device to a bond. No user interaction is required.
What is the impact of successful exploitation?
Enslaving the vxcan device can leave it half-configured under bonding. Later operations involving associated CAN sockets can dereference a null CAN receiver-list pointer and crash the kernel, causing a denial of service.
Is this a valid or supported bonding configuration?
No. Bonding CAN interfaces is architecturally invalid because CAN does not use Ethernet-style MAC addressing, ARP, or standard Ethernet link-layer mechanisms.