CVE-2026-10636

In Zephyr's IPv4 IGMP implementation, igmpsend() in subsys/net/ip/igmp.c read the network interface back out of the packet via netpktiface(pkt) after the packet had been handed to netsenddata(). On the successful-send path the packet's last reference may already have been released by the L2 driver or by the network stack's TX handling (synchronously in the default NETTCTXCOUNT=0 immediate-transmit configuration), returning the netpkt slab block to its free list. The subsequent netpktiface(pkt) dereferences the freed packet, a use-after-free read; with CONFIGNETSTATISTICSPER_INTERFACE the resulting dangling interface pointer is further dereferenced for a statistics-counter write.

The IGMP send path is reachable without authentication from inbound IPv4 IGMP membership queries addressed to 224.0.0.1 (netipv4igmpinput -> sendigmpreport/sendigmpv3report -> igmp_send), as well as from local multicast join/leave/rejoin operations.

Realistic impact is undefined behavior and potential denial of service (sporadic crash or stats corruption); a controllable write requires the asynchronous TX path plus a concurrent slab reuse.

The flaw was introduced with IGMPv2 support and affects releases from v2.6.0 through v4.4.0. The fix caches the interface pointer before sending. Note the analogous IPv6 MLD path (mldsend in subsys/net/ip/ipv6mld.c) retains the same unfixed pattern.