CVE-2025-38721: netfilter: ctnetlink: fix refcount leak on table dump

Q: What is the severity of CVE-2025-38721?

CVE-2025-38721 is classified as a medium severity vulnerability.

Q: How do I fix CVE-2025-38721?

To fix CVE-2025-38721, update the Linux kernel to the latest patched version.

Q: What systems are affected by CVE-2025-38721?

CVE-2025-38721 affects various versions of the Linux kernel that use the netfilter module.

Q: What are the consequences of exploiting CVE-2025-38721?

Exploitation of CVE-2025-38721 may lead to denial of service due to the reference count leak.

Q: When was CVE-2025-38721 published?

CVE-2025-38721 was published in 2025 and addresses a specific vulnerability in the Linux kernel.

Published Sep 4, 2025

Updated

In the Linux kernel, the following vulnerability has been resolved:

netfilter: ctnetlink: fix refcount leak on table dump

There is a reference count leak in ctnetlinkdumptable(): if (res < 0) { nfconntrackget(&ct->ctgeneral); // HERE cb->args[1] = (unsigned long)ct; ...

While its very unlikely, its possible that ct == last. If this happens, then the refcount of ct was already incremented. This 2nd increment is never undone.

This prevents the conntrack object from being released, which in turn keeps prevents cnet->count from dropping back to 0.

This will then block the netns dismantle (or conntrack rmmod) as nfconntrackcleanupnetlist() will wait forever.

This can be reproduced by running conntrackresize.sh selftest in a loop. It takes ~20 minutes for me on a preemptible kernel on average before I see a runaway kworker spinning in nfconntrackcleanupnetlist.

One fix would to change this to: if (res < 0) { if (ct != last) nfconntrackget(&ct->ctgeneral);

But this reference counting isn't needed in the first place. We can just store a cookie value instead.

A followup patch will do the same for ctnetlinkexpdumptable, it looks to me as if this has the same problem and like ctnetlinkdumptable, we only need a 'skip hint', not the actual object so we can apply the same cookie strategy there as well.

Affected Software

256 affected componentsFixes available

Linux Kernel

Microsoft azl3 kernel 6.6.96.2-1

Microsoft azl3 kernel 6.6.96.2-2

Patch available

Microsoft cbl2 kernel 5.15.186.1-1

Patch available

Linux Linux kernel>=2.6.19<5.4.297

Linux Linux kernel>=5.5<5.10.241

Linux Linux kernel>=5.11<5.15.190

Linux Linux kernel>=5.16<6.1.149

Linux Linux kernel>=6.2<6.6.103

Linux Linux kernel>=6.7<6.12.43

Linux Linux kernel>=6.13<6.15.11

Linux Linux kernel>=6.16<6.16.2

Linux Linux kernel=2.6.18

Linux Linux kernel=2.6.18-rc5

Linux Linux kernel=2.6.18-rc6

Linux Linux kernel=2.6.18-rc7

Linux Linux kernel=6.17-rc1

Debian Debian Linux=11.0

debian/linux<6.1.153-1

6.1.153-1

debian/linux<6.12.43-1

6.12.43-1

debian/linux<6.16.3-1

6.16.3-1

ubuntu/linux*

ubuntu/linux-aws*

ubuntu/linux-azure*

ubuntu/linux-lts-xenial*

ubuntu/linux*

ubuntu/linux-aws*

ubuntu/linux-aws-hwe*

ubuntu/linux-azure*

ubuntu/linux-gcp*

ubuntu/linux-hwe*

ubuntu/linux-hwe-edge*

ubuntu/linux-kvm*

ubuntu/linux-oracle*

ubuntu/linux-fips*

ubuntu/linux*

ubuntu/linux-aws*

ubuntu/linux-aws-5.0*

ubuntu/linux-aws-5.3*

ubuntu/linux-aws-5.4*

ubuntu/linux-azure*

ubuntu/linux-azure-4.15*

ubuntu/linux-azure-5.3*

ubuntu/linux-azure-5.4*

ubuntu/linux-azure-edge*

ubuntu/linux-gcp*

ubuntu/linux-gcp-4.15*

ubuntu/linux-gcp-5.3*

ubuntu/linux-gcp-5.4*

ubuntu/linux-gke-4.15*

ubuntu/linux-gke-5.4*

ubuntu/linux-gkeop-5.4*

ubuntu/linux-hwe*

ubuntu/linux-hwe-5.4*

ubuntu/linux-hwe-edge*

ubuntu/linux-ibm-5.4*

ubuntu/linux-kvm*

ubuntu/linux-oem*

ubuntu/linux-oracle*

ubuntu/linux-oracle-5.0*

ubuntu/linux-oracle-5.3*

ubuntu/linux-oracle-5.4*

ubuntu/linux-raspi-5.4*

ubuntu/linux-aws-fips*

ubuntu/linux-azure-fips*

ubuntu/linux-fips*

ubuntu/linux-gcp-fips*

ubuntu/linux-aws-fips*

ubuntu/linux-azure-fips*

ubuntu/linux-fips*

ubuntu/linux-gcp-fips*

ubuntu/linux*

ubuntu/linux-aws*

ubuntu/linux-aws-5.11*

ubuntu/linux-aws-5.13*

ubuntu/linux-aws-5.15<5.15.0-1097.104~20.04.1

5.15.0-1097.104~20.04.1

ubuntu/linux-aws-5.8*

ubuntu/linux-azure*

ubuntu/linux-azure-5.11*

ubuntu/linux-azure-5.13*

ubuntu/linux-azure-5.15<5.15.0-1102.111~20.04.1

5.15.0-1102.111~20.04.1

ubuntu/linux-azure-5.8*

ubuntu/linux-azure-fde*

ubuntu/linux-bluefield*

ubuntu/linux-gcp*

ubuntu/linux-gcp-5.11*

ubuntu/linux-gcp-5.13*

ubuntu/linux-gcp-5.15<5.15.0-1097.106~20.04.1

5.15.0-1097.106~20.04.1

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-5.15<5.15.0-163.173~20.04.1

5.15.0-163.173~20.04.1

ubuntu/linux-hwe-5.8*

ubuntu/linux-ibm*

ubuntu/linux-ibm-5.15<5.15.0-1091.94~20.04.1

5.15.0-1091.94~20.04.1

ubuntu/linux-intel-5.13*

ubuntu/linux-intel-iotg-5.15<5.15.0-1092.98~20.04.1

5.15.0-1092.98~20.04.1

ubuntu/linux-iot*

ubuntu/linux-kvm*

ubuntu/linux-lowlatency-hwe-5.15<5.15.0-163.173~20.04.1

5.15.0-163.173~20.04.1

ubuntu/linux-nvidia-tegra-5.15<5.15.0-1049.49~20.04.1

5.15.0-1049.49~20.04.1

ubuntu/linux-oem-5.10*

ubuntu/linux-oem-5.13*

ubuntu/linux-oem-5.6*

ubuntu/linux-oracle*

ubuntu/linux-oracle-5.11*

ubuntu/linux-oracle-5.13*

ubuntu/linux-oracle-5.15<5.15.0-1094.100~20.04.1

5.15.0-1094.100~20.04.1

ubuntu/linux-oracle-5.8*

ubuntu/linux-raspi*

ubuntu/linux-raspi2*

ubuntu/linux-riscv*

ubuntu/linux-riscv-5.11*

ubuntu/linux-riscv-5.15<5.15.0-1092.96~20.04.1

5.15.0-1092.96~20.04.1

ubuntu/linux-riscv-5.8*

ubuntu/linux-xilinx-zynqmp*

ubuntu/linux-aws-fips*

ubuntu/linux-azure-fips*

ubuntu/linux-fips*

ubuntu/linux-gcp-fips*

ubuntu/linux-aws-fips*

ubuntu/linux-azure-fips*

ubuntu/linux-fips*

ubuntu/linux-gcp-fips*

ubuntu/linux<5.15.0-163.173

5.15.0-163.173

ubuntu/linux-allwinner-5.19*

ubuntu/linux-aws<5.15.0-1097.104

5.15.0-1097.104

ubuntu/linux-aws-5.19*

ubuntu/linux-aws-6.2*

ubuntu/linux-aws-6.5*

ubuntu/linux-aws-6.8<6.8.0-1046.49~22.04.1

6.8.0-1046.49~22.04.1

ubuntu/linux-azure<5.15.0-1101.110

5.15.0-1101.110

ubuntu/linux-azure-5.19*

ubuntu/linux-azure-6.2*

ubuntu/linux-azure-6.5*

ubuntu/linux-azure-6.8<6.8.0-1051.57~22.04.1

6.8.0-1051.57~22.04.1

ubuntu/linux-azure-fde<5.15.0-1102.111.1

5.15.0-1102.111.1

ubuntu/linux-azure-fde-5.19*

ubuntu/linux-azure-fde-6.2*

ubuntu/linux-azure-fde-6.8<6.8.0-1046.53~22.04.1

6.8.0-1046.53~22.04.1

ubuntu/linux-gcp<5.15.0-1097.106

5.15.0-1097.106

ubuntu/linux-gcp-5.19*

ubuntu/linux-gcp-6.2*

ubuntu/linux-gcp-6.5*

ubuntu/linux-gcp-6.8<6.8.0-1047.50~22.04.2

6.8.0-1047.50~22.04.2

ubuntu/linux-gke<5.15.0-1093.99

5.15.0-1093.99

ubuntu/linux-gkeop<5.15.0-1080.88

5.15.0-1080.88

ubuntu/linux-hwe-5.19*

ubuntu/linux-hwe-6.2*

ubuntu/linux-hwe-6.5*

ubuntu/linux-hwe-6.8<6.8.0-100.100~22.04.1

6.8.0-100.100~22.04.1

ubuntu/linux-ibm<5.15.0-1091.94

5.15.0-1091.94

ubuntu/linux-ibm-6.8<6.8.0-1044.44~22.04.1

6.8.0-1044.44~22.04.1

ubuntu/linux-intel-iot-realtime*

ubuntu/linux-intel-iotg<5.15.0-1092.98

5.15.0-1092.98

ubuntu/linux-kvm<5.15.0-1089.94

5.15.0-1089.94

ubuntu/linux-lowlatency<5.15.0-163.173

5.15.0-163.173

ubuntu/linux-lowlatency-hwe-5.19*

ubuntu/linux-lowlatency-hwe-6.2*

ubuntu/linux-lowlatency-hwe-6.5*

ubuntu/linux-lowlatency-hwe-6.8<6.8.0-100.100.1~22.04.1

6.8.0-100.100.1~22.04.1

ubuntu/linux-nvidia<5.15.0-1092.93

5.15.0-1092.93

ubuntu/linux-nvidia-6.2*

ubuntu/linux-nvidia-6.5*

ubuntu/linux-nvidia-6.8<6.8.0-1046.49~22.04.1

6.8.0-1046.49~22.04.1

ubuntu/linux-nvidia-tegra<5.15.0-1049.49

5.15.0-1049.49

ubuntu/linux-nvidia-tegra-igx<5.15.0-1038.38

5.15.0-1038.38

ubuntu/linux-oem-5.17*

ubuntu/linux-oem-6.0*

ubuntu/linux-oem-6.1*

ubuntu/linux-oem-6.5*

ubuntu/linux-oracle<5.15.0-1094.100

5.15.0-1094.100

ubuntu/linux-oracle-6.5*

ubuntu/linux-oracle-6.8<6.8.0-1043.44~22.04.1

6.8.0-1043.44~22.04.1

ubuntu/linux-raspi<5.15.0-1091.94

5.15.0-1091.94

ubuntu/linux-realtime*

ubuntu/linux-riscv*

ubuntu/linux-riscv-5.19*

ubuntu/linux-riscv-6.5*

ubuntu/linux-riscv-6.8<6.8.0-100.100~22.04.1

6.8.0-100.100~22.04.1

ubuntu/linux-starfive-5.19*

ubuntu/linux-starfive-6.2*

ubuntu/linux-starfive-6.5*

ubuntu/linux-xilinx-zynqmp<5.15.0-1061.65

5.15.0-1061.65

ubuntu/linux-bluefield<5.15.0-1081.83

5.15.0-1081.83

ubuntu/linux-intel-iot-realtime<5.15.0-1089.91

5.15.0-1089.91

ubuntu/linux-realtime<5.15.0-1096.105

5.15.0-1096.105

ubuntu/linux-realtime-6.8<6.8.1-1041.42~22.04.1

6.8.1-1041.42~22.04.1

ubuntu/linux-aws-fips*

ubuntu/linux-azure-fips*

ubuntu/linux-fips*

ubuntu/linux-gcp-fips*

ubuntu/linux-aws-fips<5.15.0-1097.104+fips1

5.15.0-1097.104+fips1

ubuntu/linux-azure-fips<5.15.0-1101.110+fips1

5.15.0-1101.110+fips1

ubuntu/linux-fips<5.15.0-163.173+fips1

5.15.0-163.173+fips1

ubuntu/linux-gcp-fips<5.15.0-1097.106+fips1

5.15.0-1097.106+fips1

ubuntu/linux<6.8.0-100.100

6.8.0-100.100

ubuntu/linux-aws<6.8.0-1046.49

6.8.0-1046.49

ubuntu/linux-aws-6.14*

ubuntu/linux-azure<6.8.0-1046.52

6.8.0-1046.52

ubuntu/linux-azure-6.11*

ubuntu/linux-azure-6.14*

ubuntu/linux-azure-fde<6.8.0-1046.53

6.8.0-1046.53

ubuntu/linux-azure-fde-6.14*

ubuntu/linux-azure-nvidia<6.8.0-1039.42

6.8.0-1039.42

ubuntu/linux-azure-nvidia-6.14*

ubuntu/linux-gcp<6.8.0-1047.50

6.8.0-1047.50

ubuntu/linux-gcp-6.11*

ubuntu/linux-gcp-6.14*

ubuntu/linux-gke<6.8.0-1043.48

6.8.0-1043.48

ubuntu/linux-gkeop<6.8.0-1030.33

6.8.0-1030.33

ubuntu/linux-hwe-6.11*

ubuntu/linux-hwe-6.14*

ubuntu/linux-ibm<6.8.0-1044.44

6.8.0-1044.44

ubuntu/linux-intel*

ubuntu/linux-lowlatency<6.8.0-100.100.1

6.8.0-100.100.1

ubuntu/linux-lowlatency-hwe-6.11*

ubuntu/linux-nvidia<6.8.0-1046.49

6.8.0-1046.49

ubuntu/linux-nvidia-6.11*

ubuntu/linux-nvidia-lowlatency<6.8.0-1046.49.1

6.8.0-1046.49.1

ubuntu/linux-nvidia-tegra<6.8.0-1020.20

6.8.0-1020.20

ubuntu/linux-oem-6.11*

ubuntu/linux-oem-6.14*

ubuntu/linux-oem-6.8*

ubuntu/linux-oracle<6.8.0-1043.44

6.8.0-1043.44

ubuntu/linux-oracle-6.14*

ubuntu/linux-raspi<6.8.0-1047.51

6.8.0-1047.51

ubuntu/linux-raspi-realtime*

ubuntu/linux-realtime*

ubuntu/linux-riscv*

ubuntu/linux-riscv-6.14*

ubuntu/linux-xilinx<6.8.0-1023.24

6.8.0-1023.24

ubuntu/linux-bluefield<6.8.0-1016.20

6.8.0-1016.20

ubuntu/linux-raspi-realtime<6.8.0-2037.38

6.8.0-2037.38

ubuntu/linux-realtime<6.8.1-1041.42

6.8.1-1041.42

ubuntu/linux-realtime-6.14*

ubuntu/linux-aws-fips<6.8.0-1046.49+fips1

6.8.0-1046.49+fips1

ubuntu/linux-azure-fips<6.8.0-1046.52+fips1

6.8.0-1046.52+fips1

ubuntu/linux-fips<6.8.0-100.100+fips1

6.8.0-100.100+fips1

ubuntu/linux-gcp-fips<6.8.0-1047.50+fips1

6.8.0-1047.50+fips1

ubuntu/linux-azure-fde*

ubuntu/linux-vmware*

linux/kernel>=2.6.18<5.4.297

5.4.297

linux/kernel>=5.5.0<5.10.241

5.10.241

linux/kernel>=5.11.0<5.15.190

5.15.190

linux/kernel>=5.16.0<6.1.149

6.1.149

linux/kernel>=6.2.0<6.6.103

6.6.103

linux/kernel>=6.7.0<6.12.43

6.12.43

linux/kernel>=6.13.0<6.15.11

6.15.11

linux/kernel>=6.16.0<6.16.2

6.16.2

debian/linux

6.1.176-16.1.190-16.12.107-16.12.116-17.2.15-17.3.4-1

Remediation

Recommended actions to resolve this vulnerability, in priority order.

Upgrade
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Fixed in 6.1.153-1
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Fixed in 6.12.43-1
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Fixed in 6.16.3-1
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Fixed in 5.15.0-1097.104~20.04.1
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Fixed in 5.15.0-1102.111~20.04.1
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Fixed in 5.15.0-1097.106~20.04.1
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Fixed in 5.15.0-163.173~20.04.1
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Fixed in 5.15.0-1091.94~20.04.1
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Fixed in 5.15.0-1092.98~20.04.1
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Fixed in 5.15.0-163.173~20.04.1
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Fixed in 5.15.0-1049.49~20.04.1
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Fixed in 5.15.0-1094.100~20.04.1
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Fixed in 5.15.0-1092.96~20.04.1
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Fixed in 5.15.0-163.173
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Fixed in 5.15.0-1097.104
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Fixed in 6.8.0-1046.49~22.04.1
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Fixed in 5.15.0-1101.110
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Fixed in 6.8.0-1051.57~22.04.1
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Fixed in 5.15.0-1102.111.1
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Fixed in 6.8.0-1046.53~22.04.1
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Fixed in 5.15.0-1097.106
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Fixed in 6.8.0-1047.50~22.04.2
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Fixed in 5.15.0-1093.99
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Fixed in 5.15.0-1080.88
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Fixed in 6.8.0-100.100~22.04.1
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Fixed in 5.15.0-1091.94
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Fixed in 6.8.0-1044.44~22.04.1
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Fixed in 5.15.0-1092.98
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Fixed in 5.15.0-1089.94
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Fixed in 5.15.0-163.173
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Fixed in 6.8.0-100.100.1~22.04.1
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Fixed in 5.15.0-1092.93
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Fixed in 6.8.0-1046.49~22.04.1
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Fixed in 5.15.0-1038.38
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Fixed in 5.15.0-1094.100
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Fixed in 5.15.0-1091.94
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Fixed in 6.8.0-100.100~22.04.1
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Fixed in 5.15.0-1061.65
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Fixed in 5.15.0-1081.83
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Fixed in 5.15.0-1089.91
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Fixed in 5.15.0-1096.105
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Fixed in 6.8.1-1041.42~22.04.1
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Fixed in 5.15.0-1097.104+fips1
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Fixed in 5.15.0-1101.110+fips1
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Fixed in 5.15.0-163.173+fips1
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Fixed in 5.15.0-1097.106+fips1
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Fixed in 6.8.0-100.100
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Fixed in 6.8.0-1046.49
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Fixed in 6.8.0-1046.52
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Fixed in 6.8.0-1046.53
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Fixed in 6.8.0-1039.42
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Fixed in 6.8.0-1047.50
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Fixed in 6.8.0-1043.48
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Fixed in 6.8.0-1030.33
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Fixed in 6.8.0-1044.44
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Fixed in 6.8.0-100.100.1
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Fixed in 6.8.0-1046.49
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Fixed in 6.8.0-1046.49.1
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Fixed in 6.8.0-1020.20
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Fixed in 6.8.0-1043.44
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Fixed in 6.8.0-1047.51
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Fixed in 6.8.0-1023.24
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Fixed in 6.8.0-1016.20
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Fixed in 6.8.0-2037.38
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Fixed in 6.8.1-1041.42
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Fixed in 6.8.0-1046.49+fips1
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Fixed in 6.8.0-1046.52+fips1
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Fixed in 6.8.0-100.100+fips1
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Fixed in 6.8.0-1047.50+fips1
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Fixed in 5.4.297
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Fixed in 5.10.241
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Fixed in 5.15.190
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Fixed in 6.1.149
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Fixed in 6.6.103
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Fixed in 6.12.43
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Fixed in 6.15.11
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Fixed in 6.16.2
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Fixed in 6.1.176-1Fixed in 6.1.190-1Fixed in 6.12.107-1Fixed in 6.12.116-1Fixed in 7.2.15-1Fixed in 7.3.4-1

Event History

Sep 4, 2025

CVE Published

via MITRE·03:33 PM

Data Sourced

via MITRE·03:33 PM

Description

Data Sourced

via OSV·03:33 PM

DescriptionAffected Software

Data Sourced

via NVD·04:15 PM

RemedyDescriptionSeverityAffected Software

Sep 6, 2025

Data Sourced

via Microsoft·01:10 AM

DescriptionSeverityWeaknessAffected Software

Nov 11, 2026

Data Sourced

via OSV·09:39 AM

Severity

Parent advisories

This vulnerability appears in the following advisories.

DSA-6009

Peer vulnerabilities

Found alongside the following vulnerabilities.

Frequently Asked Questions

What is the severity of CVE-2025-38721?

CVE-2025-38721 is classified as a medium severity vulnerability.

How do I fix CVE-2025-38721?

To fix CVE-2025-38721, update the Linux kernel to the latest patched version.

What systems are affected by CVE-2025-38721?

CVE-2025-38721 affects various versions of the Linux kernel that use the netfilter module.

What are the consequences of exploiting CVE-2025-38721?

Exploitation of CVE-2025-38721 may lead to denial of service due to the reference count leak.

When was CVE-2025-38721 published?

CVE-2025-38721 was published in 2025 and addresses a specific vulnerability in the Linux kernel.

CVE-2025-38721: netfilter: ctnetlink: fix refcount leak on table dump

Affected Software

Remediation

Event History

Parent advisories

Peer vulnerabilities

Frequently Asked Questions

What is the severity of CVE-2025-38721?

How do I fix CVE-2025-38721?

What systems are affected by CVE-2025-38721?

What are the consequences of exploiting CVE-2025-38721?

When was CVE-2025-38721 published?

Company

Resources

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