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CVE Record

CVE-2025-39939: iommu/s390: Fix memory corruption when using identity domain

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.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux kernel flaw can corrupt memory on IBM Z/s390 systems when a PCI device uses an identity IOMMU domain. Reading device statistics may access an invalid domain structure. The supplied CVSS score is 7.8, reflecting potentially serious confidentiality, integrity, and availability consequences, but exposure appears limited to this specific architecture and configuration.

Executive priority

Treat as high priority for affected s390 infrastructure, especially shared or sensitive systems where local low-privilege users exist. General Linux fleets outside s390 are not shown as exposed by the supplied evidence. First determine configuration reachability, then patch through the operating-system vendor's supported channel.

Technical view

zpci_get_iommu_ctrs() incorrectly converts an identity IOMMU domain to s390_domain, although identity domains lack that backing structure. This produces an invalid address that is initially zeroed and later read through sysfs. KASAN detected a global out-of-bounds access in zpci_fmb_enable_device. The documented correction returns NULL because identity domains do not require these counters.

Likely exposure

Likely exposure is limited to Linux on s390 systems with PCI devices assigned to identity IOMMU domains. The source lists Linux 6.15, 6.16.9, and 6.17 as affected, but its version data also contains an unexplained "0" entry. Distribution backport status is not provided and must be checked separately.

Exploitation context

The CVSS vector requires local access and low privileges, with no user interaction. The supplied sources report KASAN discovery, not exploitation. This CVE is not listed as KEV in the bundle, and no cited evidence establishes active exploitation or a public exploit.

Researcher notes

The demonstrated failure is a KASAN global out-of-bounds condition caused by an invalid domain conversion. The bundle does not explain reliable exploitability, affected distribution packages, or complete release boundaries. Researchers should distinguish the observed memory-safety violation from the broader CVSS impact assumptions and verify each vendor's backport lineage.

Mitigation direction

  • Apply a vendor-supported kernel containing the referenced upstream or stable correction.
  • Check distribution advisories for backported fixes and exact affected package versions.
  • Prioritize s390 hosts using PCI identity IOMMU domains.
  • Where operationally safe, avoid identity-domain assignments until affected kernels are remediated.

Validation and detection

  • Inventory Linux kernel versions across IBM Z and other s390 systems.
  • Identify PCI devices configured with identity IOMMU domains.
  • Confirm the installed kernel includes either referenced correction or a vendor backport.
  • Review kernel diagnostics for KASAN or out-of-bounds reports involving zpci_fmb_enable_device.
  • Recheck device-statistics access after updating, using normal defensive testing procedures.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2025-39939 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.8 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
0ADP providers
3Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2025-39939Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux64af12c6ec3afd7d44bc8b2044eee59f98059087, 64af12c6ec3afd7d44bc8b2044eee59f98059087unaffected
LinuxLinux6.15, 0, 6.16.9, 6.17affected
Weakness

CWE details

No CWE listed

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