CVE-2025-38248

/// Technical description

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

bridge: mcast: Fix use-after-free during router port configuration

The bridge maintains a global list of ports behind which a multicast

router resides. The list is consulted during forwarding to ensure

multicast packets are forwarded to these ports even if the ports are not

member in the matching MDB entry.

When per-VLAN multicast snooping is enabled, the per-port multicast

context is disabled on each port and the port is removed from the global

router port list:

# ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1

# ip link add name dummy1 up master br1 type dummy

# ip link set dev dummy1 type bridge_slave mcast_router 2

$ bridge -d mdb show | grep router

router ports on br1: dummy1

# ip link set dev br1 type bridge mcast_vlan_snooping 1

$ bridge -d mdb show | grep router

However, the port can be re-added to the global list even when per-VLAN

multicast snooping is enabled:

# ip link se

/// 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