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Vulnerability record · CVE-2025-39939 · published 4 October 2025

CVE-2025-39939: Linux kernel out-of-bounds write vulnerability

Linux · Linux Kernel

In the Linux kernel, the following vulnerability has been resolved: iommu/s390: Fix memory corruption when using identity domain zpci_get_iommu_ctrs() returns counter information to be reported as part of device statistics; these counters are stored as part of the s390_domain. The problem, however, is that the identity domain is not backed by an s390_domain and so the conversion via to_s390_domain() yields a bad address that is zero'd initially and read on-demand later via a sysfs read. These counters aren't necessary for the identity domain; just return NULL in this case. This issue was discovered via KASAN with reports that look like: BUG: KASAN: global-out-of-bounds in zpci_fmb_enable_device when using the identity domain for a device on s390.

7.8 CVSS 3.1 High EPSS 0.14% · top 97.0% CWE-787 · Out-of-bounds write
7.8CVSS 3.1 base score
0.14%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
30 Jul 2026Last modified by NVD

Description

In the Linux kernel, the following vulnerability has been resolved: iommu/s390: Fix memory corruption when using identity domain zpci_get_iommu_ctrs() returns counter information to be reported as part of device statistics; these counters are stored as part of the s390_domain. The problem, however, is that the identity domain is not backed by an s390_domain and so the conversion via to_s390_domain() yields a bad address that is zero'd initially and read on-demand later via a sysfs read. These counters aren't necessary for the identity domain; just return NULL in this case. This issue was discovered via KASAN with reports that look like: BUG: KASAN: global-out-of-bounds in zpci_fmb_enable_device when using the identity domain for a device on s390.

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://git.kernel.org/stable/c/17a58caf3863163c4a84a218a9649be2c8061443 Patch
https://git.kernel.org/stable/c/b3506e9bcc777ed6af2ab631c86a9990ed97b474 Patch

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Source: NIST National Vulnerability Database (record CVE-2025-39939), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.