{"id":"CVE-2026-81003","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-81003","generatedAt":"2026-10-28T03:27:38.714Z","title":"In the Linux kernel, the following vulnerability has been resolved: net/iucv: filter frames in afiucv_hs_rcv() by ingress device afiucv_hs_rcv() selects a socket from iucv_sk_list by matching four 8-byte name fields in the transport header alone.","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.","published":"2026-09-11T20:19:09.000Z","lastModified":"2026-10-19T09:17:34.000Z","status":"Received","sourceIdentifier":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","cvss":{"version":"3.1","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"},"cwe":[],"affected":[],"epss":{"score":0.00309,"percentile":0.23568,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.31%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://git.kernel.org/stable/c/0a5af67e7184c6a0e155c317840bd64b37177af4","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/639828ad4d374056167391dbaffd13dd5e5e5ddb","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/712330f8a4293cfd97b0d62b7c7dc01862a16b98","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/80230a18c164a4b5bbc048fe2768b219ac17bc5a","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/8e3763f1ccac3fc395f9af2b87114c023ced8a3f","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/92e5c281f1caa287bb58292f2687c9e3ff3aa23e","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/a7f0130a091724e69827ab58e74777a88747e892","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/dfac2936b83be00035ae176f8252e1c1e1de9207","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-81003","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}