{"cve":"CVE-2026-81003","nvd":{"published":"2026-09-11T20:19:08.863","modified":"2026-10-19T09:17:33.500","status":"Received","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H","score":8.1},"cwes":[],"references":["https://git.kernel.org/stable/c/0a5af67e7184c6a0e155c317840bd64b37177af4","https://git.kernel.org/stable/c/639828ad4d374056167391dbaffd13dd5e5e5ddb","https://git.kernel.org/stable/c/712330f8a4293cfd97b0d62b7c7dc01862a16b98","https://git.kernel.org/stable/c/80230a18c164a4b5bbc048fe2768b219ac17bc5a","https://git.kernel.org/stable/c/8e3763f1ccac3fc395f9af2b87114c023ced8a3f"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:53:43.293028046+00:00"},"epss":{"cve":"CVE-2026-81003","score":0.00309,"percentile":0.23549,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}