CVE-2025-71097
MediumCVSS 5.5Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
A reference count leak was discovered in the Linux kernel when deleting nexthop objects for IPv4 error routes (e.g., blackhole). Error routes were not flushed with the dead nexthop, keeping references on the nexthop object and device, preventing their release.
Risk Assessment
This leak can prevent network interfaces (e.g., dummy) from being deleted, causing resource exhaustion and potential network availability issues for the organization.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit in stable branch). If an update is not possible, avoid deleting nexthop objects while error routes with nhid exist.
Original NVD description (English source)
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.