{"id":"CVE-2026-99133","aliases":[],"title":"net/iucv: fix the recvmsg window update","titleSource":"Linux","descriptionSource":"Linux","products":[{"vendor":"Linux","name":"Linux","platforms":[],"versions":[{"version":"3881ac441f642d56503818123446f7298442236b","status":"affected","lessThan":"8f2efa742f4cfe7dd756154f8bc07350dbe3ec92","versionType":"git"},{"version":"3881ac441f642d56503818123446f7298442236b","status":"affected","lessThan":"fe7393a627db2d093e8c0cae69d619b30fefae5f","versionType":"git"},{"version":"3881ac441f642d56503818123446f7298442236b","status":"affected","lessThan":"fa5acd038ea657ad5033713d6916214cbd349151","versionType":"git"}],"defaultStatus":"unaffected","source":"Linux","url":"https://www.cve.org/CVERecord?id=CVE-2026-99133"},{"vendor":"Linux","name":"Linux","platforms":[],"versions":[{"version":"3.2","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.2","versionType":"semver"},{"version":"6.18.59","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.13","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"defaultStatus":"affected","source":"Linux","url":"https://www.cve.org/CVERecord?id=CVE-2026-99133"}],"remediation":[],"description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/iucv: fix the recvmsg window update\n\niucv_sock_recvmsg() sends the HiperSockets-only AF_IUCV_FLAG_WIN without\ntesting the transport, so on a classic z/VM socket iucv_send_ctrl() sizes\nthe skb through a NULL iucv->hs_dev. SO_MSGLIMIT accepts 1, so msglimit / 2\nis zero and one recvmsg() on its own socket is enough for an unprivileged\nprocess to take a spurious disconnect.\n\nIt also calls iucv_send_ctrl() under spin_lock_bh(&message_q.lock), which\nallocates GFP_KERNEL inside a section the code treats as atomic. Sending\noutside that lock lets two recvmsg() reach afiucv_hs_send() at once, where\nmsg_recv is sampled for the advertised window and subtracted after\ndev_queue_xmit() -- and sendmsg reaches that counter under lock_sock()\nwhile recvmsg holds no socket lock, so both can subtract the same value,\nthe counter goes negative and the credit reaches the peer twice.\n\nTest the transport, claim the credit with atomic_xchg() after the last\nerror exit and hand it back if the transmit fails, and send once the lock\nis dropped.","severity":"unknown","score":null,"published":"2026-10-28T10:34:46.398Z","modified":"2026-10-28T10:34:46.398Z","withdrawn":false,"knownExploited":false,"affected":[],"references":["https://git.kernel.org/stable/c/8f2efa742f4cfe7dd756154f8bc07350dbe3ec92","https://git.kernel.org/stable/c/fe7393a627db2d093e8c0cae69d619b30fefae5f","https://git.kernel.org/stable/c/fa5acd038ea657ad5033713d6916214cbd349151"],"sources":[{"name":"CVE","id":"CVE-2026-99133","modified":"2026-10-28T10:34:46.398Z","url":"https://www.cve.org/CVERecord?id=CVE-2026-99133"}],"assessments":[],"sourceAffected":[],"kev":{"status":"not-listed","checkedAt":"2026-10-29T02:20:33.012Z"},"coverage":[{"source":"NVD","status":"not-checked"},{"source":"GHSA","status":"not-checked"},{"source":"EUVD","status":"not-checked"},{"source":"EPSS","status":"not-checked"}],"evidence":[]}