{
 "finding_id": "DF-3507",
 "status": "reproduced",
 "reproduced": 1,
 "impact": "denial_of_service",
 "confidence": "certain",
 "verdict": "Reproduced on the minimally-repaired harness module (constructor UB fix only - the stock module cannot even create a node, see DF-3506 pack). Sequence (fechg dump evidence): (1) tap0+tap1 added to fec0 - FECDMP shows tap0 ac_netgraph=0xfffff801179b28a0 == fec0's node. (2) A SECOND bundle fec1 was created and ADD_IFACE tap0 issued against it - the duplicate check at ng_fec.c:362-369 only scans THIS bundle's ports, so the add SUCCEEDED (rc=0) and tap0's ac_netgraph silently switched to fec1's node (0xfffff8011752ea00) while fec0's portlist still contains tap0: cross-bundle enslavement + silent RX ownership theft confirmed. (3) DEL_IFACE tap0 from fec1 - ng_fec_delport (:417-471) never clears the member's ac_netgraph: FECDMP shows tap0 still pointing at fec1's node after fec1 no longer lists it (stale ownership). The freed-node dereference arm (rmnode sets node->private=NULL at :1239 then frees; ng_fec_input:752-758 would deref the stale IFP2NG) is code-certain but could not be run: ng_fec_rmnode/stop paths additionally hit the INVARIANTS-only lwkt_serializer assert ('panic: assertion IS_SERIALIZED in lwkt_serialize_exit' from ng_fec_stop, captured in boot.log) and crash before creating the dangling state - on production (non-INVARIANTS) kernels the teardown runs and the stale pointer survives. Also note v1 ng_fec shares ac_netgraph with ng_ether(4) (if_arp.h:124), so fec+ng_ether coexistence silently steals RX exactly as filed. Root-gated misconfiguration-turned-DoS; no escalation path (fixed-offset reads of freed slab; NULL private in the benign case).",
 "exploit_chain": "",
 "evidence": "fec-sequence.log (three FECDMP snapshots: after adds / after cross-enslave / after DEL_IFACE showing tap0 ac_netgraph unchanged), fechg.c",
 "kernel_refs": [
  "sys/netgraph/fec/ng_fec.c:362",
  "sys/netgraph/fec/ng_fec.c:379",
  "sys/netgraph/fec/ng_fec.c:417",
  "sys/netgraph/fec/ng_fec.c:752",
  "sys/netgraph/fec/ng_fec.c:1239"
 ],
 "poc_changes": "harness module (ctor-UB fix + sysctl driver + delport member-ioctl serialize-wrap for INVARIANTS context) - cross-enslave/delport logic verbatim",
 "attempts": 4,
 "guest_uname": "DragonFly dfbsd 6.5-DEVELOPMENT #0: Thu Jul  2 06:02:54 UTC 2026 root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC x86_64",
 "runtime_sec": 900,
 "guest_dirty": 0,
 "build_cmd": "cd /usr/src/sys/netgraph/fec && make   # fechg.c staged as ng_fec.c",
 "run_cmd": "sysctl kern.fechg.op=create x2; ADD_IFACE tap0 to fec0 and fec1; DEL_IFACE tap0 from fec1; sysctl kern.fechg.dump",
 "code_hash": "40c03b5b50a8d27e39d27b40ddb2af0af84a6c0778c121aeae364684bd18ed85",
 "notes": "cross-bundle check absent: only same-bundle TAILQ scanned (:362). The stale ac_netgraph after DEL_IFACE is the deterministic, runtime-proven core of this finding.",
 "recommended_fix": "in ng_fec_addport refuse interfaces whose ac_netgraph is already non-NULL (or whose if_input is already ng_fec_input); in ng_fec_delport clear ac_netgraph when it still points at this bundle's node."
}