CVE-2026-99133: Linux 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.

Metrics

EPSS Probability

0.17%

6.9th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 3881ac441f642d56503818123446f7298442236b, < 01123990f59ce32a1a5e690a4aeee002e932bb07; >= 3881ac441f642d56503818123446f7298442236b, < 1ebe68bbf8e75eeccaca0c7bc9694f5bc0c3f00a; >= 3881ac441f642d56503818123446f7298442236b, < 23e7fbbdca5aaba2a9a7bb9e4f2dc179c290ee76; >= 3881ac441f642d56503818123446f7298442236b, < ce8aac3eb57f5366fa082b7cb8a1ac5652274f37; >= 3881ac441f642d56503818123446f7298442236b, < 8f2efa742f4cfe7dd756154f8bc07350dbe3ec92; >= 3881ac441f642d56503818123446f7298442236b, < fe7393a627db2d093e8c0cae69d619b30fefae5f; >= 3881ac441f642d56503818123446f7298442236b, < fa5acd038ea657ad5033713d6916214cbd349151
Linux	Linux	3.2

References

Timeline

Published: Oct 28, 2026
Last Modified: Oct 30, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-99133?

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.

How severe is CVE-2026-99133?

Severity scoring for CVE-2026-99133 is pending analysis. The EPSS model estimates a 0.17% probability of exploitation in the next 30 days.

How do I fix CVE-2026-99133?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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