CVE-2025-71097

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References