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CVE Record

CVE-2025-39815: RISC-V: KVM: fix stack overrun when loading vlenb

In the Linux kernel, the following vulnerability has been resolved: RISC-V: KVM: fix stack overrun when loading vlenb The userspace load can put up to 2048 bits into an xlen bit stack buffer. We want only xlen bits, so check the size beforehand.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A flaw in Linux KVM on RISC-V can let a locally privileged user provide oversized vector-length data that overruns a kernel stack buffer. Successful exploitation could compromise confidentiality, integrity, and availability. Systems not using RISC-V KVM are unlikely to be exposed.

Executive priority

Treat as high priority where RISC-V KVM hosts process untrusted workloads or provide local access. Patch through normal emergency kernel maintenance after compatibility testing. Organizations without RISC-V KVM exposure should document non-applicability rather than initiate broad emergency action.

Technical view

The KVM RISC-V vlenb loading path accepted up to 2048 bits from userspace into an xlen-sized stack buffer. The resolved implementation checks the supplied size before loading it. The supplied CVSS 3.1 score is 7.8, requiring local access and low privileges, with no user interaction.

Likely exposure

Exposure is concentrated in affected Linux versions running KVM on RISC-V. The bundle identifies versions 6.8, 6.12.45, 6.16.5, and 6.17 as affected, but its version data is incomplete or ambiguous. Confirm distribution-specific status and backports with the kernel or operating-system vendor.

Exploitation context

The CVSS vector indicates local, low-privileged exploitation with low complexity and no user interaction. The source bundle does not establish remote exploitation or active exploitation in the wild, and the CVE is not listed as KEV.

Researcher notes

The defect is a stack overrun caused by a size mismatch between userspace-supplied vector data and an xlen-sized destination. No CWE is supplied. The record supports severe potential impact but does not establish reliable exploitation, observed attacks, or a particular post-corruption outcome. Affected-version boundaries require vendor confirmation.

Mitigation direction

  • Update to a vendor-supported kernel containing the referenced size-check fix.
  • Prioritize RISC-V hosts that run KVM or permit untrusted local users.
  • Consult distribution advisories for fixed package versions and backported patches.
  • Restrict unnecessary local and virtualization access until affected systems are updated.

Validation and detection

  • Inventory Linux systems using RISC-V architecture and KVM virtualization.
  • Compare installed kernel builds against vendor advisories and referenced stable commits.
  • Confirm the deployed kernel includes the vlenb input-size validation fix.
  • Retest KVM workloads after updating and monitor hosts for abnormal kernel failures.
Prepared
Confidence
medium
Sources
5

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

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

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CVE-2025-39815 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.

2CVSS vectors
3Timeline events
1ADP providers
4Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

2 official scores

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
5.5CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2025-39815Attack 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.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux2fa290372dfe7dd248b1c16f943f273a3e674f22, 2fa290372dfe7dd248b1c16f943f273a3e674f22, 2fa290372dfe7dd248b1c16f943f273a3e674f22unaffected
LinuxLinux6.8, 0, 6.12.45, 6.16.5, 6.17affected
Weakness

CWE details

No CWE listed

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