Linux kernel net/iucv recvmsg window update flaw causes disconnects
Key facts
- Attack vector
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- Privileges required
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- User interaction
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- Attack complexity
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- Impact type
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- Confidentiality · integrity · availability
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- Fix status
- Partial Red Hat: 7 without a fix
No CVSS vector from any source. Fix status from CNA and Red Hat.
Summary
The Linux kernel net/iucv code sends a HiperSockets window update during recvmsg without testing the transport, so on classic z/VM sockets it can cause a spurious disconnect. An unprivileged process can trigger this with a single recvmsg call. A race in the same path can also let the window credit be counted twice.
Written with Claude Haiku 5.5 from the sources below · 2026-10-30
Description from the CNA
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.
Why it matters now
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
Remediation
Upgrade to Linux kernel 5.15.224, 6.1.191, 6.6.161, 6.12.115, 6.18.59, 7.2.13 or 7.3. Red Hat Enterprise Linux 6 has no fix planned, and Red Hat Enterprise Linux 7, 8, 9 and 10 and OpenShift Container Platform 4 and 5 have no fix available.
Written with Claude Haiku 5.5 from the sources below · 2026-10-30
- Fix · CNA Linux (Linux) Fixed in 5.15.224, 6.1.191, 6.6.161, 6.12.115, 6.18.59, 7.2.13, 7.3
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 10 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 8 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 9 | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Container Platform 4 | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Container Platform 5 | Affected | No fix yet: Fix deferred |
Timeline
- 2026-10-28 Threatist record created from CVE-2026-99133
- 2026-10-28 Alias added: GHSA-j8jx-fcfm-v8gr
- 2026-10-29 Affected versions changed · Red Hat
- 2026-10-29 CVSS score added · Red Hat
- 2026-10-30 Affected versions changed · Red Hat
- 2026-10-30 Fix available: Linux/Linux@01123990f59ce32a1a5e690a4aeee002e932bb07, Linux/Linux@1ebe68bbf8e75eeccaca0c7bc9694f5bc0c3f00a, Linux/Linux@23e7fbbdca5aaba2a9a7bb9e4f2dc179c290ee76 +5 · CNA
- 2026-10-30 4 new references · CNA
References
Other 7
- 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/ce8aac3eb57f5366fa082b7cb8a1ac5652274f37
- https://git.kernel.org/stable/c/8f2efa742f4cfe7dd756154f8bc07350dbe3ec92
- https://git.kernel.org/stable/c/fe7393a627db2d093e8c0cae69d619b30fefae5f
- https://git.kernel.org/stable/c/fa5acd038ea657ad5033713d6916214cbd349151
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Sources
- CVE-2026-99133 · CVE Program
- CVE-2026-99133 · NVD
- FIRST EPSS
- GHSA-j8jx-fcfm-v8gr · GitHub Advisory Database · CC BY 4.0
- CVE-2026-99133 · Red Hat security data · CC BY 4.0
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