CVE-2025-38721
netfilter: ctnetlink: fix refcount leak on table dump
Published Sep 4, 2025
CVSS 3.1 · 5.5 Medium
EPSS < 1%
KEV · Not listed
Description
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 ctnetlink_dump_table():
if (res < 0) {
nf_conntrack_get(&ct->ct_general); // 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
nf_conntrack_cleanup_net_list() will wait forever.
This can be reproduced by running conntrack_resize.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 nf_conntrack_cleanup_net_list.
One fix would to change this to:
if (res < 0) {
if (ct != last)
nf_conntrack_get(&ct->ct_general);
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 ctnetlink_exp_dump_table,
it looks to me as if this has the same problem and like
ctnetlink_dump_table, we only need a 'skip hint', not the actual
object so we can apply the same cookie strategy there as well.
netfilter: ctnetlink: fix refcount leak on table dump
There is a reference count leak in ctnetlink_dump_table():
if (res < 0) {
nf_conntrack_get(&ct->ct_general); // 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
nf_conntrack_cleanup_net_list() will wait forever.
This can be reproduced by running conntrack_resize.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 nf_conntrack_cleanup_net_list.
One fix would to change this to:
if (res < 0) {
if (ct != last)
nf_conntrack_get(&ct->ct_general);
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 ctnetlink_exp_dump_table,
it looks to me as if this has the same problem and like
ctnetlink_dump_table, we only need a 'skip hint', not the actual
object so we can apply the same cookie strategy there as well.
Affected Products
-
CVE record
-
NVD configurations
-
Red Hat packages
No data
-
OpenCVE enrichment
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
||||||||||||||||||||||||||||||||||||
| Linux | Linux | affected |
|
Configuration 1 [-]
|
Configuration 2 [-]
|
No data.
| Vendor | Product | Versions |
|---|---|---|
| Linux | Linux Kernel | — |
Remediation
Tracking
Advisories
| Source | ID | Title |
|---|---|---|
 Debian DLA |
DLA-4327-1 | linux security update |
| Debian DLA |
DLA-4328-1 | linux-6.1 security update |
 Debian DSA |
DSA-6009-1 | linux security update |
 EUVD |
EUVD-2025-26748 | 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 ctnetlink_dump_table(): if (res < 0) { nf_conntrack_get(&ct->ct_general); // 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 nf_conntrack_cleanup_net_list() will wait forever. This can be reproduced by running conntrack_resize.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 nf_conntrack_cleanup_net_list. One fix would to change this to: if (res < 0) { if (ct != last) nf_conntrack_get(&ct->ct_general); 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 ctnetlink_exp_dump_table, it looks to me as if this has the same problem and like ctnetlink_dump_table, we only need a 'skip hint', not the actual object so we can apply the same cookie strategy there as well. |
 Ubuntu USN |
USN-7909-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-7909-2 | Linux kernel (Real-time) vulnerabilities |
| Ubuntu USN |
USN-7909-3 | Linux kernel (FIPS) vulnerabilities |
| Ubuntu USN |
USN-7910-1 | Linux kernel (Azure FIPS) vulnerabilities |
| Ubuntu USN |
USN-7909-4 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-7910-2 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-7909-5 | Linux kernel (Raspberry Pi) vulnerabilities |
| Ubuntu USN |
USN-7933-1 | Linux kernel (KVM) vulnerabilities |
| Ubuntu USN |
USN-7938-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-8028-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-8028-2 | Linux kernel (Real-time) vulnerabilities |
| Ubuntu USN |
USN-8031-1 | Linux kernel (GCP) vulnerabilities |
| Ubuntu USN |
USN-8028-3 | Linux kernel (Real-time) vulnerabilities |
| Ubuntu USN |
USN-8028-4 | Linux kernel (FIPS) vulnerabilities |
| Ubuntu USN |
USN-8028-5 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-8031-2 | Linux kernel (GCP FIPS) vulnerabilities |
| Ubuntu USN |
USN-8028-6 | Linux kernel (HWE) vulnerabilities |
| Ubuntu USN |
USN-8031-3 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-8052-1 | Linux kernel (Low Latency) vulnerabilities |
| Ubuntu USN |
USN-8028-7 | Linux kernel (Low Latency NVIDIA) vulnerabilities |
| Ubuntu USN |
USN-8028-8 | Linux kernel (IBM) vulnerabilities |
| Ubuntu USN |
USN-8052-2 | Linux kernel (Xilinx) vulnerabilities |
| Ubuntu USN |
USN-8074-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-8074-2 | Linux kernel (Azure FIPS) vulnerabilities |
| Ubuntu USN |
USN-8126-1 | Linux kernel (Azure) vulnerabilities |
Metrics
No CVSS v4.0
Attack Vector Local
Attack Complexity Low
Privileges Required Low
Scope Unchanged
Confidentiality Impact None
Integrity Impact None
Availability Impact High
User Interaction None
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.177% probability within 30 days)
Exploitation none
Automatable no
Technical Impact partial
References
History
Nov 6, 2026 7:30 PM
Scoring metrics updated
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ssvc
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Oct 15, 2026 2:30 AM
Added references
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May 12, 2026 1:30 PM
Added references
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Jan 9, 2026 4:00 PM
First appearance in the feed. Weaknesses updated. Affected versions updated. Affected vendors updated
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| Type | Values Removed | Values Added |
|---|---|---|
| First Time appeared |
Debian
Debian debian Linux |
|
| Weaknesses | NVD-CWE-Other | |
| CPEs | cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.18:-:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.18:rc5:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.18:rc6:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.18:rc7:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.17:rc1:*:*:*:*:*:* |
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| Vendors & Products |
Debian
Debian debian Linux |
Nov 3, 2025 6:30 PM
Added references
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| Type | Values Removed | Values Added |
|---|---|---|
| References |
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Sep 5, 2025 2:15 PM
First appearance in the feed. Affected vendors updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| First Time appeared |
Linux
Linux linux Kernel |
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| Vendors & Products |
Linux
Linux linux Kernel |
Sep 5, 2025 12:15 AM
Added references. Scoring metrics updated
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| Type | Values Removed | Values Added |
|---|---|---|
| References |
| |
| Metrics |
threat_severity
|
cvssV3_1
|
Sep 4, 2025 3:45 PM
Description updated. Title updated. Added references
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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 ctnetlink_dump_table(): if (res < 0) { nf_conntrack_get(&ct->ct_general); // 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 nf_conntrack_cleanup_net_list() will wait forever. This can be reproduced by running conntrack_resize.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 nf_conntrack_cleanup_net_list. One fix would to change this to: if (res < 0) { if (ct != last) nf_conntrack_get(&ct->ct_general); 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 ctnetlink_exp_dump_table, it looks to me as if this has the same problem and like ctnetlink_dump_table, we only need a 'skip hint', not the actual object so we can apply the same cookie strategy there as well. | |
| Title | netfilter: ctnetlink: fix refcount leak on table dump | |
| References |
|
|
Subscriptions
Weaknesses
