UBUNTU-CVE-2026-64417: Null Pointer Dereference

Q: Who can trigger this issue?

A local user with sufficient access to write to the relevant kernel debugfs shrinker file can trigger it. The provided crash example involves the xen-backend shrinker, whose scan callback is absent.

Q: What is the impact of successful exploitation?

Writing to a debugfs file for a callback that the shrinker does not implement can invoke a NULL function pointer and panic the kernel. This results in a local denial of service.

Q: Are all debugfs shrinker files affected?

No. The issue applies when shrinker_debugfs_add() creates a count or scan file for a shrinker that lacks the corresponding count_objects() or scan_objects() callback. The scan path is demonstrated, and the count path has the same potential issue.

Q: What changes in the resolved version?

The fix creates count and scan debugfs files only when the corresponding shrinker callbacks are present, preventing writes from reaching NULL callback pointers.

Published Jul 25, 2026

Updated

In the Linux kernel, the following vulnerability has been resolved: mm: shrinker: fix NULL pointer dereference in debugfs shrinkerdebugfsadd() creates both "count" and "scan" debugfs files unconditionally. That assumes every shrinker implements both countobjects() and scanobjects(), which is not guaranteed. For example, the xen-backend shrinker sets countobjects() but leaves scanobjects() NULL, so writing to its scan file calls through a NULL function pointer and panics the kernel: BUG: kernel NULL pointer dereference, address: 0000000000000000 RIP: 0010:0x0 Code: Unable to access opcode bytes at 0xffffffffffffffd6. Call Trace: <TASK> shrinkerdebugfsscanwrite+0x12e/0x270 fullproxywrite+0x5f/0x90 vfswrite+0xde/0x420 ? filpflush+0x75/0x90 ? filpclose+0x1d/0x30 ? dodup2+0xb8/0x120 ksyswrite+0x68/0xf0 ? filpflush+0x75/0x90 dosyscall64+0xb3/0x5b0 entrySYSCALL64afterhwframe+0x76/0x7e The count path has the same issue in principle if a shrinker omits countobjects(). To fix it, only create "count" and "scan" debugfs files when the corresponding callbacks are present.

Affected Software

161 affected componentsFixes available

ubuntu/linux-hwe-edge*

ubuntu/linux-aws-5.0*

ubuntu/linux-aws-5.3*

ubuntu/linux-azure*

ubuntu/linux-azure-5.3*

ubuntu/linux-azure-edge*

ubuntu/linux-gcp*

ubuntu/linux-gcp-5.3*

ubuntu/linux-gke-4.15*

ubuntu/linux-gke-5.4*

ubuntu/linux-gkeop-5.4*

ubuntu/linux-hwe*

ubuntu/linux-hwe-edge*

ubuntu/linux-oem*

ubuntu/linux-oracle-5.0*

ubuntu/linux-oracle-5.3*

ubuntu/linux-aws-5.11*

ubuntu/linux-aws-5.13*

ubuntu/linux-aws-5.8*

ubuntu/linux-azure-5.11*

ubuntu/linux-azure-5.13*

ubuntu/linux-azure-5.8*

ubuntu/linux-azure-fde*

ubuntu/linux-gcp-5.11*

ubuntu/linux-gcp-5.13*

ubuntu/linux-gcp-5.8*

ubuntu/linux-gke*

ubuntu/linux-gke-5.15*

ubuntu/linux-gkeop*

ubuntu/linux-gkeop-5.15*

ubuntu/linux-hwe-5.11*

ubuntu/linux-hwe-5.13*

ubuntu/linux-hwe-5.8*

ubuntu/linux-intel-5.13*

ubuntu/linux-oem-5.10*

ubuntu/linux-oem-5.13*

ubuntu/linux-oem-5.6*

ubuntu/linux-oracle-5.11*

ubuntu/linux-oracle-5.13*

ubuntu/linux-oracle-5.8*

ubuntu/linux-raspi2*

ubuntu/linux-riscv*

ubuntu/linux-riscv-5.11*

ubuntu/linux-riscv-5.8*

ubuntu/linux-allwinner-5.19*

ubuntu/linux-aws-5.19*

ubuntu/linux-aws-6.2*

ubuntu/linux-aws-6.5*

ubuntu/linux-aws-6.8*

ubuntu/linux-azure-5.19*

ubuntu/linux-azure-6.2*

ubuntu/linux-azure-6.5*

ubuntu/linux-azure-6.8*

ubuntu/linux-azure-fde-5.19*

ubuntu/linux-azure-fde-6.2*

ubuntu/linux-azure-fde-6.8*

ubuntu/linux-gcp-5.19*

ubuntu/linux-gcp-6.2*

ubuntu/linux-gcp-6.5*

ubuntu/linux-gcp-6.8*

ubuntu/linux-hwe-5.19*

ubuntu/linux-hwe-6.2*

ubuntu/linux-hwe-6.5*

ubuntu/linux-ibm-6.8*

ubuntu/linux-intel-iot-realtime*

ubuntu/linux-lowlatency-hwe-5.19*

ubuntu/linux-lowlatency-hwe-6.2*

ubuntu/linux-lowlatency-hwe-6.5*

ubuntu/linux-lowlatency-hwe-6.8*

ubuntu/linux-nvidia-6.2*

ubuntu/linux-nvidia-6.5*

ubuntu/linux-nvidia-6.8*

ubuntu/linux-oem-5.17*

ubuntu/linux-oem-6.0*

ubuntu/linux-oem-6.1*

ubuntu/linux-oem-6.5*

ubuntu/linux-oracle-6.5*

ubuntu/linux-oracle-6.8*

ubuntu/linux-realtime*

ubuntu/linux-riscv*

ubuntu/linux-riscv-5.19*

ubuntu/linux-riscv-6.5*

ubuntu/linux-riscv-6.8*

ubuntu/linux-starfive-5.19*

ubuntu/linux-starfive-6.2*

ubuntu/linux-starfive-6.5*

ubuntu/linux-realtime-6.8*

ubuntu/linux<6.8.0-147.147

6.8.0-147.147

ubuntu/linux-aws<6.8.0-1067.70

6.8.0-1067.70

ubuntu/linux-aws-6.14*

ubuntu/linux-aws-6.17*

ubuntu/linux-aws-7.0<7.0.0-1012.12~24.04.1

7.0.0-1012.12~24.04.1

ubuntu/linux-azure<6.8.0-1071.79

6.8.0-1071.79

ubuntu/linux-azure-6.11*

ubuntu/linux-azure-6.14*

ubuntu/linux-azure-6.17*

ubuntu/linux-azure-7.0<7.0.0-1014.14~24.04.1

7.0.0-1014.14~24.04.1

ubuntu/linux-azure-fde<6.8.0-1069.76

6.8.0-1069.76

ubuntu/linux-azure-fde-6.14*

ubuntu/linux-azure-fde-6.17*

ubuntu/linux-azure-fde-7.0<7.0.0-1013.13~24.04.1

7.0.0-1013.13~24.04.1

ubuntu/linux-azure-nvidia*

ubuntu/linux-azure-nvidia-6.14*

ubuntu/linux-gcp<6.8.0-1071.79

6.8.0-1071.79

ubuntu/linux-gcp-6.11*

ubuntu/linux-gcp-6.14*

ubuntu/linux-gcp-7.0<7.0.0-1011.11~24.04.1

7.0.0-1011.11~24.04.1

ubuntu/linux-gke<6.8.0-1066.74

6.8.0-1066.74

ubuntu/linux-gkeop<6.8.0-1052.56

6.8.0-1052.56

ubuntu/linux-hwe-6.11*

ubuntu/linux-hwe-6.14*

ubuntu/linux-hwe-6.17*

ubuntu/linux-hwe-7.0<7.0.0-31.31~24.04.1

7.0.0-31.31~24.04.1

ubuntu/linux-ibm<6.8.0-1067.68

6.8.0-1067.68

ubuntu/linux-lowlatency<6.8.0-147.147.1

6.8.0-147.147.1

ubuntu/linux-lowlatency-hwe-6.11*

ubuntu/linux-nvidia*

ubuntu/linux-nvidia-6.11*

ubuntu/linux-nvidia-6.17*

ubuntu/linux-nvidia-7.0<7.0.0-1018.18~24.04.1

7.0.0-1018.18~24.04.1

ubuntu/linux-nvidia-lowlatency*

ubuntu/linux-nvidia-tegra*

ubuntu/linux-oem-6.11*

ubuntu/linux-oem-6.14*

ubuntu/linux-oem-6.17*

ubuntu/linux-oem-6.8*

ubuntu/linux-oracle<6.8.0-1064.67

6.8.0-1064.67

ubuntu/linux-oracle-6.14*

ubuntu/linux-oracle-6.17*

ubuntu/linux-oracle-7.0<7.0.0-1011.11~24.04.1

7.0.0-1011.11~24.04.1

ubuntu/linux-raspi*

ubuntu/linux-raspi-realtime*

ubuntu/linux-realtime*

ubuntu/linux-riscv*

ubuntu/linux-riscv-6.14*

ubuntu/linux-riscv-6.17*

ubuntu/linux-riscv-7.0<7.0.0-31.31.1~24.04.1

7.0.0-31.31.1~24.04.1

ubuntu/linux-xilinx*

ubuntu/linux-bluefield<6.8.0-1033.38

6.8.0-1033.38

ubuntu/linux-raspi-realtime*

ubuntu/linux-realtime<6.8.1-1062.63

6.8.1-1062.63

ubuntu/linux-realtime-6.14*

ubuntu/linux-realtime-6.17*

ubuntu/linux-aws-fips<6.8.0-1067.70+fips1

6.8.0-1067.70+fips1

ubuntu/linux-azure-fips<6.8.0-1071.79+fips1

6.8.0-1071.79+fips1

ubuntu/linux-fips<6.8.0-147.147+fips1

6.8.0-147.147+fips1

ubuntu/linux-gcp-fips<6.8.0-1071.79+fips1

6.8.0-1071.79+fips1

ubuntu/linux<7.0.0-31.31

7.0.0-31.31

ubuntu/linux-aws<7.0.0-1012.12

7.0.0-1012.12

ubuntu/linux-azure<7.0.0-1014.14

7.0.0-1014.14

ubuntu/linux-azure-fde<7.0.0-1013.13

7.0.0-1013.13

ubuntu/linux-gcp<7.0.0-1011.11

7.0.0-1011.11

ubuntu/linux-gke<7.0.0-1006.7

7.0.0-1006.7

ubuntu/linux-ibm<7.0.0-1013.13

7.0.0-1013.13

ubuntu/linux-nvidia<7.0.0-1018.18

7.0.0-1018.18

ubuntu/linux-nvidia-bos<7.0.0-2018.18

7.0.0-2018.18

ubuntu/linux-oem-7.0<7.0.0-1013.13

7.0.0-1013.13

ubuntu/linux-oracle<7.0.0-1011.11

7.0.0-1011.11

ubuntu/linux-raspi<7.0.0-1019.19

7.0.0-1019.19

ubuntu/linux-realtime<7.0.0-31.31.1

7.0.0-31.31.1

ubuntu/linux-riscv<7.0.0-31.31.1

7.0.0-31.31.1

Remediation

Recommended actions to resolve this vulnerability, in priority order.

Upgrade
Upgrade ubuntu/linux to a version that resolves this vulnerability.
Fixed in 6.8.0-147.147
Upgrade
Upgrade ubuntu/linux-aws to a version that resolves this vulnerability.
Fixed in 6.8.0-1067.70
Upgrade
Upgrade ubuntu/linux-aws-7.0 to a version that resolves this vulnerability.
Fixed in 7.0.0-1012.12~24.04.1
Upgrade
Upgrade ubuntu/linux-azure to a version that resolves this vulnerability.
Fixed in 6.8.0-1071.79
Upgrade
Upgrade ubuntu/linux-azure-7.0 to a version that resolves this vulnerability.
Fixed in 7.0.0-1014.14~24.04.1
Upgrade
Upgrade ubuntu/linux-azure-fde to a version that resolves this vulnerability.
Fixed in 6.8.0-1069.76
Upgrade
Upgrade ubuntu/linux-azure-fde-7.0 to a version that resolves this vulnerability.
Fixed in 7.0.0-1013.13~24.04.1
Upgrade
Upgrade ubuntu/linux-gcp to a version that resolves this vulnerability.
Fixed in 6.8.0-1071.79
Upgrade
Upgrade ubuntu/linux-gcp-7.0 to a version that resolves this vulnerability.
Fixed in 7.0.0-1011.11~24.04.1
Upgrade
Upgrade ubuntu/linux-gke to a version that resolves this vulnerability.
Fixed in 6.8.0-1066.74
Upgrade
Upgrade ubuntu/linux-gkeop to a version that resolves this vulnerability.
Fixed in 6.8.0-1052.56
Upgrade
Upgrade ubuntu/linux-hwe-7.0 to a version that resolves this vulnerability.
Fixed in 7.0.0-31.31~24.04.1
Upgrade
Upgrade ubuntu/linux-ibm to a version that resolves this vulnerability.
Fixed in 6.8.0-1067.68
Upgrade
Upgrade ubuntu/linux-lowlatency to a version that resolves this vulnerability.
Fixed in 6.8.0-147.147.1
Upgrade
Upgrade ubuntu/linux-nvidia-7.0 to a version that resolves this vulnerability.
Fixed in 7.0.0-1018.18~24.04.1
Upgrade
Upgrade ubuntu/linux-oracle to a version that resolves this vulnerability.
Fixed in 6.8.0-1064.67
Upgrade
Upgrade ubuntu/linux-oracle-7.0 to a version that resolves this vulnerability.
Fixed in 7.0.0-1011.11~24.04.1
Upgrade
Upgrade ubuntu/linux-riscv-7.0 to a version that resolves this vulnerability.
Fixed in 7.0.0-31.31.1~24.04.1
Upgrade
Upgrade ubuntu/linux-bluefield to a version that resolves this vulnerability.
Fixed in 6.8.0-1033.38
Upgrade
Upgrade ubuntu/linux-realtime to a version that resolves this vulnerability.
Fixed in 6.8.1-1062.63
Upgrade
Upgrade ubuntu/linux-aws-fips to a version that resolves this vulnerability.
Fixed in 6.8.0-1067.70+fips1
Upgrade
Upgrade ubuntu/linux-azure-fips to a version that resolves this vulnerability.
Fixed in 6.8.0-1071.79+fips1
Upgrade
Upgrade ubuntu/linux-fips to a version that resolves this vulnerability.
Fixed in 6.8.0-147.147+fips1
Upgrade
Upgrade ubuntu/linux-gcp-fips to a version that resolves this vulnerability.
Fixed in 6.8.0-1071.79+fips1
Upgrade
Upgrade ubuntu/linux to a version that resolves this vulnerability.
Fixed in 7.0.0-31.31
Upgrade
Upgrade ubuntu/linux-aws to a version that resolves this vulnerability.
Fixed in 7.0.0-1012.12
Upgrade
Upgrade ubuntu/linux-azure to a version that resolves this vulnerability.
Fixed in 7.0.0-1014.14
Upgrade
Upgrade ubuntu/linux-azure-fde to a version that resolves this vulnerability.
Fixed in 7.0.0-1013.13
Upgrade
Upgrade ubuntu/linux-gcp to a version that resolves this vulnerability.
Fixed in 7.0.0-1011.11
Upgrade
Upgrade ubuntu/linux-gke to a version that resolves this vulnerability.
Fixed in 7.0.0-1006.7
Upgrade
Upgrade ubuntu/linux-ibm to a version that resolves this vulnerability.
Fixed in 7.0.0-1013.13
Upgrade
Upgrade ubuntu/linux-nvidia to a version that resolves this vulnerability.
Fixed in 7.0.0-1018.18
Upgrade
Upgrade ubuntu/linux-nvidia-bos to a version that resolves this vulnerability.
Fixed in 7.0.0-2018.18
Upgrade
Upgrade ubuntu/linux-oem-7.0 to a version that resolves this vulnerability.
Fixed in 7.0.0-1013.13
Upgrade
Upgrade ubuntu/linux-oracle to a version that resolves this vulnerability.
Fixed in 7.0.0-1011.11
Upgrade
Upgrade ubuntu/linux-raspi to a version that resolves this vulnerability.
Fixed in 7.0.0-1019.19
Upgrade
Upgrade ubuntu/linux-realtime to a version that resolves this vulnerability.
Fixed in 7.0.0-31.31.1
Upgrade
Upgrade ubuntu/linux-riscv to a version that resolves this vulnerability.
Fixed in 7.0.0-31.31.1

Event History

Jul 25, 2026

CVE Published

via OSV·10:17 AM

Data Sourced

via OSV·10:17 AM

DescriptionSeverityAffected Software

Frequently Asked Questions

Who can trigger this issue?

A local user with sufficient access to write to the relevant kernel debugfs shrinker file can trigger it. The provided crash example involves the xen-backend shrinker, whose scan callback is absent.

What is the impact of successful exploitation?

Writing to a debugfs file for a callback that the shrinker does not implement can invoke a NULL function pointer and panic the kernel. This results in a local denial of service.

Are all debugfs shrinker files affected?

No. The issue applies when shrinker_debugfs_add() creates a count or scan file for a shrinker that lacks the corresponding count_objects() or scan_objects() callback. The scan path is demonstrated, and the count path has the same potential issue.

What changes in the resolved version?

The fix creates count and scan debugfs files only when the corresponding shrinker callbacks are present, preventing writes from reaching NULL callback pointers.

UBUNTU-CVE-2026-64417: Null Pointer Dereference

Affected Software

Remediation

Event History

Frequently Asked Questions

Who can trigger this issue?

What is the impact of successful exploitation?

Are all debugfs shrinker files affected?

What changes in the resolved version?

Company

Resources

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