UBUNTU-CVE-2026-43288: Medium severity ubuntu/linux-aws vulnerability
In the Linux kernel, the following vulnerability has been resolved: ext4: move ext4percpuparaminit() before ext4mbinit() When running kvm-xfstests -c ext4/1k -C 1 generic/383 with the DOUBLECHECK macro defined, the following panic is triggered: ================================================================== EXT4-fs error (device vdc): ext4validateblockbitmap:423: comm mount: bg 0: bad block bitmap checksum BUG: unable to handle page fault for address: ff110000fa2cc000 PGD 3e01067 P4D 3e02067 PUD 0 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 0 UID: 0 PID: 2386 Comm: mount Tainted: G W 6.18.0-gba65a4e7120a-dirty #1152 PREEMPT(none) RIP: 0010:percpucounteraddbatch+0x13/0xa0 Call Trace: <TASK> ext4markgroupbitmapcorrupted+0xcb/0xe0 ext4validateblockbitmap+0x2a1/0x2f0 ext4readblockbitmap+0x33/0x50 mbgroupbbbitmapalloc+0x33/0x80 ext4mbaddgroupinfo+0x190/0x250 ext4mbinitbackend+0x87/0x290 ext4mbinit+0x456/0x640 ext4fillsuper+0x1072/0x1680 ext4fillsuper+0xd3/0x280 gettreebdevflags+0x132/0x1d0 vfsgettree+0x29/0xd0 vfscmdcreate+0x59/0xe0 dosysfsconfig+0x4f6/0x6b0 dosyscall64+0x50/0x1f0 entrySYSCALL64afterhwframe+0x76/0x7e ================================================================== This issue can be reproduced using the following commands: mkfs.ext4 -F -q -b 1024 /dev/sda 5G tune2fs -O quota,project /dev/sda mount /dev/sda /tmp/test With DOUBLECHECK defined, mbgroupbbbitmapalloc() reads and validates the block bitmap. When the validation fails, ext4markgroupbitmapcorrupted() attempts to update sbi->sfreeclusterscounter. However, this percpucounter has not been initialized yet at this point, which leads to the panic described above. Fix this by moving the execution of ext4percpuparaminit() to occur before ext4mbinit(), ensuring the per-CPU counters are initialized before they are used.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
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ubuntu/linux-aws-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1060.63~22.04.1 - Upgrade
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ubuntu/linux-azure-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1063.71~22.04.1 - Upgrade
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ubuntu/linux-azure-fde-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1062.69~22.04.1 - Upgrade
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ubuntu/linux-gcp-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1063.69~22.04.1 - Upgrade
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ubuntu/linux-hwe-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-136.136~22.04.1 - Upgrade
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ubuntu/linux-ibm-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1060.61~22.04.1 - Upgrade
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ubuntu/linux-lowlatency-hwe-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-134.134.1~22.04.1 - Upgrade
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ubuntu/linux-nvidia-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1058.61~22.04.1 - Upgrade
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ubuntu/linux-oracle-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1057.58~22.04.1 - Upgrade
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ubuntu/linux-riscv-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-134.134~22.04.1 - Upgrade
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ubuntu/linux-realtime-6.8to a version that resolves this vulnerability.Fixed in 6.8.1-1055.56~22.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 6.8.0-134.134 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 6.8.0-1060.63 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 6.8.0-1063.71 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 6.8.0-1062.69 - Upgrade
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ubuntu/linux-azure-nvidiato a version that resolves this vulnerability.Fixed in 6.8.0-1039.42 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 6.8.0-1063.69 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 6.8.0-1058.64 - Upgrade
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ubuntu/linux-gkeopto a version that resolves this vulnerability.Fixed in 6.8.0-1045.48 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 6.8.0-1060.61 - Upgrade
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ubuntu/linux-lowlatencyto a version that resolves this vulnerability.Fixed in 6.8.0-134.134.1 - Upgrade
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ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 6.8.0-1058.61 - Upgrade
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ubuntu/linux-nvidia-lowlatencyto a version that resolves this vulnerability.Fixed in 6.8.0-1058.61.1 - Upgrade
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ubuntu/linux-nvidia-tegrato a version that resolves this vulnerability.Fixed in 6.8.0-1029.30 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 6.8.0-1057.58 - Upgrade
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ubuntu/linux-raspito a version that resolves this vulnerability.Fixed in 6.8.0-1060.64 - Upgrade
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ubuntu/linux-xilinxto a version that resolves this vulnerability.Fixed in 6.8.0-1032.33 - Upgrade
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ubuntu/linux-bluefieldto a version that resolves this vulnerability.Fixed in 6.8.0-1026.30 - Upgrade
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ubuntu/linux-raspi-realtimeto a version that resolves this vulnerability.Fixed in 6.8.0-2049.50 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 6.8.1-1055.56 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1060.63+fips1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1062.69+fips1 - Upgrade
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-134.134+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1063.69+fips1 - Compensating control
Modify ext4 initialization so ext4_percpu_param_init() executes before ext4_mb_init(), ensuring the per-CPU counters are initialized before ext4_mb_init() and related bitmap validation use them.
Event History
Frequently Asked Questions
What conditions are required to trigger the failure?
The reported trigger is mounting an ext4 filesystem whose block bitmap fails checksum validation. The panic occurs during ext4 mount initialization, when corrupted block-bitmap state is handled before the relevant per-CPU parameters have been initialized.
What is the operational impact?
A local user able to cause the affected system to mount a specially malformed or corrupted ext4 filesystem may trigger a kernel page fault and panic. The provided severity vector indicates availability impact only, with no reported confidentiality or integrity impact.
Which Ubuntu kernel packages are listed as affected?
The listed software includes ubuntu/linux, ubuntu/linux-aws, ubuntu/linux-azure, ubuntu/linux-gcp, and their listed FIPS variants: ubuntu/linux-fips, ubuntu/linux-aws-fips, ubuntu/linux-azure-fips, and ubuntu/linux-gcp-fips.