UBUNTU-CVE-2026-68169: Use After Free
In the Linux kernel, the following vulnerability has been resolved: mptcp: pm: userspace: fix use-after-free in getlocalid In mptcppmuserspacegetlocalid(), the address entry is looked up under spinlock, but its id is read after dropping the lock. A concurrent deletion can free the entry between the unlock and the read, leading to UAF. The race window is narrow. It was reproduced only with a locally constructed stress test that repeatedly overlaps an MPJOIN SYN with a MPTCPPMCMDSUBFLOWDESTROY request. However, the KASAN report below confirms that the race is reachable: [ 666.319376] BUG: KASAN: slab-use-after-free in mptcpuserspacepmgetlocalid+0x1dc/0x1f0 [ 666.319386] Read of size 1 at addr ffff888124845610 by task swapper/0/0 ... [ 666.319401] Call Trace: [ 666.319405] <IRQ> [ 666.319408] dumpstacklvl+0x53/0x70 [ 666.319412] printaddressdescription.constprop.0+0x2c/0x3b0 [ 666.319418] printreport+0xbe/0x2b0 [ 666.319421] ? mptcpuserspacepmgetlocalid+0x1dc/0x1f0 [ 666.319423] kasanreport+0xce/0x100 [ 666.319426] ? mptcpuserspacepmgetlocalid+0x1dc/0x1f0 [ 666.319429] mptcpuserspacepmgetlocalid+0x1dc/0x1f0 [ 666.319433] mptcppmgetlocalid+0x371/0x440 ... [ 666.319821] Allocated by task 45539: [ 666.319844] kasansavestack+0x33/0x60 [ 666.319855] kasansavetrack+0x14/0x30 [ 666.319858] kasankmalloc+0x8f/0xa0 [ 666.319863] kmallocnoprof+0x1e7/0x520 [ 666.319867] sockkmalloc+0xdf/0x130 [ 666.319885] sockkmemdup+0x1b/0x40 [ 666.319888] mptcpuserspacepmappendnewlocaladdr+0x261/0x500 [ 666.319910] mptcppmnlannouncedoit+0x16a/0x610 ... [ 666.319967] Freed by task 45560: [ 666.319988] kasansavestack+0x33/0x60 [ 666.319991] kasansavetrack+0x14/0x30 [ 666.319994] kasansavefreeinfo+0x3b/0x60 [ 666.319998] kasanslabfree+0x43/0x70 [ 666.320000] kfree+0x166/0x440 [ 666.320003] sockkfrees+0x1d/0x50 [ 666.320007] mptcpuserspacepmdeletelocaladdr.isra.0+0x157/0x200 [ 666.320011] mptcppmnlsubflowdestroydoit+0x51d/0xea0 Fix by copying the id into a local variable while still holding the lock, and use -1 as a "not found" sentinel.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1069.74~22.04.1 - Upgrade
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ubuntu/linux-azure-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1073.82~22.04.1 - Upgrade
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ubuntu/linux-azure-fde-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1071.78~22.04.1 - Upgrade
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ubuntu/linux-gcp-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1073.81~22.04.1 - Upgrade
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ubuntu/linux-ibm-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1069.70~22.04.1 - Upgrade
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ubuntu/linux-lowlatency-hwe-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-149.149.1~22.04.1 - Upgrade
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ubuntu/linux-oracle-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1067.71~22.04.1 - Upgrade
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ubuntu/linux-realtime-6.8to a version that resolves this vulnerability.Fixed in 6.8.1-1064.65~22.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 6.8.0-149.149 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 6.8.0-1069.74 - Upgrade
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ubuntu/linux-aws-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1014.14~24.04.1 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 6.8.0-1073.82 - Upgrade
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ubuntu/linux-azure-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.17~24.04.1 - Upgrade
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ubuntu/linux-azure-fde-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1016.16~24.04.1 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 6.8.0-1073.81 - Upgrade
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ubuntu/linux-gcp-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1014.14~24.04.1 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 6.8.0-1068.77 - Upgrade
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ubuntu/linux-gkeopto a version that resolves this vulnerability.Fixed in 6.8.0-1053.57 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-38.38~24.04.4 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 6.8.0-1069.70 - Upgrade
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ubuntu/linux-lowlatencyto a version that resolves this vulnerability.Fixed in 6.8.0-149.149.1 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 6.8.0-1067.70 - Upgrade
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ubuntu/linux-nvidia-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1024.25~24.04.1 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 6.8.0-1067.71 - Upgrade
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ubuntu/linux-oracle-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1013.13~24.04.1 - Upgrade
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ubuntu/linux-raspito a version that resolves this vulnerability.Fixed in 6.8.0-1068.72 - Upgrade
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ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1~24.04.1 - Upgrade
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ubuntu/linux-vmwareto a version that resolves this vulnerability.Fixed in 6.8.0-1010.10 - Upgrade
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ubuntu/linux-bluefieldto a version that resolves this vulnerability.Fixed in 6.8.0-1036.41 - Upgrade
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ubuntu/linux-raspi-realtimeto a version that resolves this vulnerability.Fixed in 6.8.0-2056.58 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 6.8.1-1064.65 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1069.74+fips1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1073.82+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1073.81+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-nvidia-bosto a version that resolves this vulnerability.Fixed in 7.0.0-2022.23 - 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
Fix mptcp_pm_userspace_get_local_id() by copying the address entry ID into a local variable while still holding the spinlock, and use -1 as the "not found" sentinel.
Event History
Frequently Asked Questions
What conditions are needed to trigger this issue?
The race involves MPTCP userspace path management while an MP_JOIN SYN overlaps with an MPTCP_PM_CMD_SUBFLOW_DESTROY request. The reported reproduction required a locally constructed stress test repeatedly creating that overlap.
How likely is exploitation in normal operation?
The race window is described as narrow, and the issue was reproduced only with a local stress test. The available information does not describe a remote-only or unauthenticated exploitation path.
How can I identify whether this race has occurred?
A KASAN-enabled kernel may report a slab use-after-free in mptcp_userspace_pm_get_local_id, with a read of size 1 reported in that function. The supplied report shows the fault occurring in an IRQ context.