{"id":"CVE-2026-81003","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-81003","summary":"net/iucv: filter frames in afiucv_hs_rcv() by ingress device","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/iucv: filter frames in afiucv_hs_rcv() by ingress device\n\nafiucv_hs_rcv() selects a socket from iucv_sk_list by matching four 8-byte\nname fields in the transport header alone. No check is made against the\nnet_device the frame arrived on.\n\nThis can cause a frame arriving on any netdev to be delivered to an AF_IUCV\nsocket. Three problems follow.\n\nFirst, a frame arriving over HiperSockets can be delivered to a socket\nbound to the classic z/VM IUCV transport, which has iucv->hs_dev == NULL.\niucv_sock_bind() takes the classic path whenever the requested userid\nmatches iucv_userid, even on a guest that also has a HiperSockets device\ncarrying the same identifier. The child socket created by\nafiucv_hs_callback_syn() for such a match inherits hs_dev = NULL and\ntransport = AF_IUCV_TRANS_HIPER, so the first send() on it returns -ENODEV.\nThe socket delivered to accept() is unusable.\n\nSecond, a frame arriving on one netdev can be delivered to a socket bound\nto a different IQD device. Which can lead to\n- Accept-queue exhaustion (DoS)\n- Attacker-controlled peer identity in the child socket\n- Data injection into existing sockets\n- Fabric noise on the IQD fabric, where bogus replies are sent\n- killing established connections\n\nThird, all AF_IUCV sockets live in init_net, as iucv_sock_alloc() calls\nsk_alloc(&init_net, ...). But even frames arriving on netdev devices in a\nnamespace can be delivered to an IUCV socket. So a process in an\nunprivileged user and network namespace holding only the CAP_NET_RAW\ncapability valid within that namespace can send a raw ETH_P_AF_IUCV frame\non its own lo device and have it matched against init_net sockets.\n\nFix all three by skipping any socket whose hs_dev does not match the\ningress device. A classic z/VM IUCV socket has hs_dev == NULL; the ingress\ndev is never NULL, so classic sockets are skipped automatically. An unbound\nHIPER socket also has hs_dev == NULL and is skipped. A bound HIPER socket\nis only reachable from the exact IQD device it was bound to. Because hs_dev\nis always a device in init_net (iucv_sock_bind() scans\nfor_each_netdev_rcu(&init_net, ...) exclusively), a frame whose ingress\ndevice belongs to another namespace never matches any socket.\n\nNote that AF_IUCV over HiperSockets provides no per-connection\nauthentication: no sequence numbers, no TLS, no nonce. The four name fields\nidentifying a connection are exchanged in plaintext on the shared\nHiperSockets segment (VCHID). Any host on the same HiperSockets segment\ncould spoof any frame type against an existing connection. That is a\nprotocol-level property unchanged by this patch. The fix reduces the attack\nsurface to peers present on the same HiperSockets segment.","published":"2026-09-11T19:42:56.172Z","modified":"2026-09-14T03:46:00.655251300Z","cvss":{"score":8.1,"severity":"HIGH","vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"6.12.109"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/80230a18c164a4b5bbc048fe2768b219ac17bc5a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8e3763f1ccac3fc395f9af2b87114c023ced8a3f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a7f0130a091724e69827ab58e74777a88747e892"},{"type":"WEB","url":"https://git.kernel.org/stable/c/dfac2936b83be00035ae176f8252e1c1e1de9207"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/81xxx/CVE-2026-81003.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-81003"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-14T03:46:00.655251300Z"}}