Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: net/iucv: fix the recvmsg window update iucv_sock_recvmsg() sends the HiperSockets-only AF_IUCV_FLAG_WIN without testing the transport, so on a classic z/VM socket iucv_send_ctrl() sizes the skb through a NULL iucv->hs_dev. SO_MSGLIMIT accepts 1, so msglimit / 2 is zero and one recvmsg() on its own socket is enough for an unprivileged process to take a spurious disconnect. It also calls iucv_send_ctrl() under spin_lock_bh(&message_q.lock), which allocates GFP_KERNEL inside a section the code treats as atomic. Sending outside that lock lets two recvmsg() reach afiucv_hs_send() at once, where msg_recv is sampled for the advertised window and subtracted after dev_queue_xmit() -- and sendmsg reaches that counter under lock_sock() while recvmsg holds no socket lock, so both can subtract the same value, the counter goes negative and the credit reaches the peer twice. Test the transport, claim the credit with atomic_xchg() after the last error exit and hand it back if the transmit fails, and send once the lock is dropped.
References
- https://git.kernel.org/stable/c/01123990f59ce32a1a5e690a4aeee002e932bb07
- https://git.kernel.org/stable/c/1ebe68bbf8e75eeccaca0c7bc9694f5bc0c3f00a
- https://git.kernel.org/stable/c/23e7fbbdca5aaba2a9a7bb9e4f2dc179c290ee76
- https://git.kernel.org/stable/c/8f2efa742f4cfe7dd756154f8bc07350dbe3ec92
- https://git.kernel.org/stable/c/ce8aac3eb57f5366fa082b7cb8a1ac5652274f37
- https://git.kernel.org/stable/c/fa5acd038ea657ad5033713d6916214cbd349151
- https://git.kernel.org/stable/c/fe7393a627db2d093e8c0cae69d619b30fefae5f
FAQ
What is CVE-2026-99133?
CVE-2026-99133 is a documented vulnerability. In the Linux kernel, the following vulnerability has been resolved: net/iucv: fix the recvmsg window update iucv_sock_recvmsg() sends the HiperSockets-only AF_IUCV_FLAG_WIN without testing the trans...
How severe is CVE-2026-99133?
CVSS scoring is not yet available for CVE-2026-99133. Check NVD for updates.
Is there a patch for CVE-2026-99133?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.