VulnerabilityPublished 28 Oct 2026

CVE-2026-99133: Linux kernel · net/iucv: fix the recvmsg window update

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in fe7393a627db2d093e8c0cae69d619b30fefae5f : update Linux kernel when convenient.

Data as of 28 Oct 2026, 10:58 UTC

Severity

Unrated

Rated by Threat Radar · CVSS not yet scored by NVD

Patch: Available – fixed in fe7393a627db2d093e8c0cae69d619b30fefae5f, fa5acd038ea657ad5033713d6916214cbd349151, 8f2efa742f4cfe7dd756154f8bc07350dbe3ec92

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Linux kernel to fe7393a627db2d093e8c0cae69d619b30fefae5f, fa5acd038ea657ad5033713d6916214cbd349151 or 8f2efa742f4cfe7dd756154f8bc07350dbe3ec92.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 3881ac441f642d56503818123446f7298442236b, < fe7393a627db2d093e8c0cae69d619b30fefae5f	Fixed in fe7393a627db2d093e8c0cae69d619b30fefae5f
LinuxLinux	Affected ≥ 3881ac441f642d56503818123446f7298442236b, < fa5acd038ea657ad5033713d6916214cbd349151	Fixed in fa5acd038ea657ad5033713d6916214cbd349151
LinuxLinux	Affected ≥ 3881ac441f642d56503818123446f7298442236b, < 8f2efa742f4cfe7dd756154f8bc07350dbe3ec92	Fixed in 8f2efa742f4cfe7dd756154f8bc07350dbe3ec92
LinuxLinux	Affected =3.2	Fixed in–

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

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