CVE-2024-27415

/// Technical description

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

netfilter: bridge: confirm multicast packets before passing them up the stack

conntrack nf_confirm logic cannot handle cloned skbs referencing

the same nf_conn entry, which will happen for multicast (broadcast)

frames on bridges.

Example:

macvlan0

|

br0

/ \

ethX ethY

ethX (or Y) receives a L2 multicast or broadcast packet containing

an IP packet, flow is not yet in conntrack table.

1. skb passes through bridge and fake-ip (br_netfilter)Prerouting.

-> skb->_nfct now references a unconfirmed entry

2. skb is broad/mcast packet. bridge now passes clones out on each bridge

interface.

3. skb gets passed up the stack.

4. In macvlan case, macvlan driver retains clone(s) of the mcast skb

and schedules a work queue to send them out on the lower devices.

The clone skb->_nfct is not a copy, it is the same entry as the

original skb. The macvlan rx handler then returns RX

/// 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