CVE-2025-71097
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2026-01-13

Last updated on: 2026-03-25

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: ipv4: Fix reference count leak when using error routes with nexthop objects When a nexthop object is deleted, it is marked as dead and then fib_table_flush() is called to flush all the routes that are using the dead nexthop. The current logic in fib_table_flush() is to only flush error routes (e.g., blackhole) when it is called as part of network namespace dismantle (i.e., with flush_all=true). Therefore, error routes are not flushed when their nexthop object is deleted: # ip link add name dummy1 up type dummy # ip nexthop add id 1 dev dummy1 # ip route add 198.51.100.1/32 nhid 1 # ip route add blackhole 198.51.100.2/32 nhid 1 # ip nexthop del id 1 # ip route show blackhole 198.51.100.2 nhid 1 dev dummy1 As such, they keep holding a reference on the nexthop object which in turn holds a reference on the nexthop device, resulting in a reference count leak: # ip link del dev dummy1 [ 70.516258] unregister_netdevice: waiting for dummy1 to become free. Usage count = 2 Fix by flushing error routes when their nexthop is marked as dead. IPv6 does not suffer from this problem.
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Meta Information
Published
2026-01-13
Last Modified
2026-03-25
Generated
2026-06-16
AI Q&A
2026-01-14
EPSS Evaluated
2026-06-14
NVD
CVE-2025-71097
Affected Vendors & Products
Showing 15 associated CPEs
Vendor Product Version / Range
linux linux_kernel 5.3
linux linux_kernel From 5.11 (inc) to 5.15.198 (exc)
linux linux_kernel 6.19
linux linux_kernel 6.19
linux linux_kernel 6.19
linux linux_kernel 6.19
linux linux_kernel 6.19
linux linux_kernel From 6.13 (inc) to 6.18.4 (exc)
linux linux_kernel From 5.16 (inc) to 6.1.160 (exc)
linux linux_kernel From 6.2 (inc) to 6.6.120 (exc)
linux linux_kernel From 6.7 (inc) to 6.12.64 (exc)
linux linux_kernel 6.19
linux linux_kernel 6.19
linux linux_kernel 6.19
linux linux_kernel From 5.3.1 (inc) to 5.10.248 (exc)
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Exploitability
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CWE ID Description
CWE-UNKNOWN
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Executive Summary

This vulnerability is a reference count leak in the Linux kernel's IPv4 networking code. When a nexthop object is deleted, it is marked as dead, and the system is supposed to flush all routes using that nexthop. However, the existing logic only flushes error routes (like blackhole routes) during network namespace dismantle, not when the nexthop is deleted. As a result, error routes continue to hold references to the deleted nexthop object and its device, causing a reference count leak that prevents the device from being freed properly. This issue does not affect IPv6.

Impact Analysis

This vulnerability can cause resource leaks in the Linux kernel networking stack by preventing network devices associated with deleted nexthop objects from being freed. This can lead to increased memory usage and potentially degrade system performance or stability over time, especially in environments where nexthop objects and error routes are frequently created and deleted.

Detection Guidance

This vulnerability can be detected by checking for lingering error routes (such as blackhole routes) that still reference deleted nexthop objects. You can use the following commands to detect this condition: # ip link add name dummy1 up type dummy # ip nexthop add id 1 dev dummy1 # ip route add 198.51.100.1/32 nhid 1 # ip route add blackhole 198.51.100.2/32 nhid 1 # ip nexthop del id 1 # ip route show If you see blackhole routes still referencing the deleted nexthop (nhid 1), it indicates the reference count leak vulnerability is present. Also, attempting to delete the device with 'ip link del dev dummy1' may hang or show usage count warnings, indicating the leak.

Mitigation Strategies

To mitigate this vulnerability, ensure that your Linux kernel is updated with the fix that flushes error routes when their nexthop is marked as dead. This prevents the reference count leak. Until the fix is applied, avoid deleting nexthop objects that are still referenced by error routes, or manually flush such routes before deleting nexthops.

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