EUVD-2026-66463
GHSA-ccx7-24wp-j32x
Severity by source
AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Race condition exploitation requires precise timing so AC:H is more accurate than vendor AC:L; S:C and C/I/A:H retained given potential VM-to-host escape via vfio_ccw.
Primary rating from Vendor (Linux).
CVSS VectorVendor: Linux
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Lifecycle Timeline
5DescriptionCVE.org
In the Linux kernel, the following vulnerability has been resolved:
s390/vfio_ccw: Selectively expand io_mutex
The io_mutex was defined to serialize the io_regions, but then has also sort of been associated with the I/O themselves because of the close relationship they share.
With the handful of races that are possible, the choices are either to: A) expand the scope of io_mutex to close these remaining windows, or B) reduce the scope of io_mutex to just io_region, and introduce a new lock mechanism for the remaining I/O resources
This patch implements A, since B brings with it a lot more interactions that would need to be tracked and kept in a correct hierarchy. It also takes advantage of the workqueue element for cp_free() that now gets called out of fsm_notoper(), which could be invoked out of an interrupt context and thus cannot acquire a mutex itself.
AnalysisAI
Race conditions in the s390/vfio_ccw subsystem of the Linux kernel arise from an insufficiently scoped io_mutex that serialized io_regions but left other I/O operations unserialized, creating exploitable synchronization windows. Local low-privilege users inside guest VMs on IBM s390/zSeries hosts running vfio_ccw can exploit these races to achieve scope-changed privilege escalation into the host kernel, with full confidentiality, integrity, and availability impact. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires local low-privilege access (PR:L, AV:L per CVSS vector) to a guest VM on a host running the IBM s390/zSeries architecture with the vfio_ccw kernel module loaded and actively providing channel I/O device pass-through to that guest. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 score of 8.8 (AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H) reflects a high-severity local privilege escalation; the S:C (scope changed) metric is the critical signal, indicating that successful exploitation can break out of the guest VM boundary into the host kernel - particularly impactful in multi-tenant s390 mainframe environments. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker with low-privilege local access inside a guest VM on an IBM s390 host using vfio_ccw for channel device pass-through spawns concurrent threads submitting crafted I/O requests, racing to hit the unserialized window in io_mutex between io_region operations and interrupt-context cp_free() invocations. If the race is won, the attacker corrupts kernel state or bypasses access controls, potentially escalating to host kernel privilege. … |
| Remediation | Upgrade the Linux kernel to a patched version: 6.6.153 (commit 2a5ac0c0f1f7da33929211a2e41911bf72ee35d8), 6.12.105 (commit 34f4feff3e90bd09308fad0974e97113b23b812a), 6.18.46 (commit b6aecea4b2b246f9fbd98a5712daa1193a60818e), 7.1.10 (commit 2ba9efdf9ebedc4e54df4b56aa3b43a65f7967cd), or 7.2 (commit f72a51810d49411bd8cad0c2df8592320a2fe5cc), all available at https://git.kernel.org/stable/. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all IBM s390/zSeries systems running Linux kernel versions prior to 6.6.153, 6.12.105, 6.18.46, 7.1.10, or 7.2 and assess patch eligibility against your maintenance windows. …
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