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CVE Record

CVE-2025-21666: vsock: prevent null-ptr-deref in vsock_*[has_data|has_space]

In the Linux kernel, the following vulnerability has been resolved: vsock: prevent null-ptr-deref in vsock_*[has_data|has_space] Recent reports have shown how we sometimes call vsock_*_has_data() when a vsock socket has been de-assigned from a transport (see attached links), but we shouldn't. Previous commits should have solved the real problems, but we may have more in the future, so to avoid null-ptr-deref, we can return 0 (no space, no data available) but with a warning. This way the code should continue to run in a nearly consistent state and have a warning that allows us to debug future problems.

MediumCVSS 5.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2025-21666 is a Linux kernel vsock flaw where the kernel can hit a null pointer instead of safely handling a socket without an assigned transport. The business risk is availability: a local low-privileged user may be able to crash or destabilize affected systems, not steal data or bypass authentication.

Executive priority

Schedule remediation in the normal kernel patch cycle, with faster action for shared or virtualization-heavy systems. This is not supported as an internet-routed remote compromise in the provided evidence, but it can affect service availability.

Technical view

The issue is CWE-476 in Linux vsock data/space checks. The fix changes vsock_*_has_data() and vsock_*_has_space() behavior so de-assigned sockets return no data or space, with a warning, instead of dereferencing null transport state. CVSS is 5.5: local, low complexity, low privilege, no user interaction, high availability impact.

Likely exposure

Exposure is Linux systems running affected kernel builds with vsock functionality available, especially where local users or workloads can reach vsock sockets. The source bundle identifies Linux as affected, but exact distro package status should be verified with vendor advisories.

Exploitation context

The provided sources do not show active exploitation, and KEV is false. The CVSS vector indicates local, low-privilege exploitation with availability impact only. Treat it primarily as a denial-of-service risk on multi-user hosts, shared compute, and virtualization-heavy environments.

Researcher notes

The core condition is a vsock socket de-assigned from its transport before has_data or has_space checks. The patch is defensive: return 0 and warn rather than dereference null. Evidence is strongest for upstream Linux and downstream advisories, not for real-world exploitation.

Mitigation direction

  • Update affected Linux kernels using vendor-supported packages or stable kernel fixes.
  • Prioritize systems allowing untrusted local users, containers, or shared workloads.
  • Review Debian LTS and Siemens advisories if those distributions or products apply.
  • If no vendor package is available, monitor vendor guidance before applying kernel changes.

Validation and detection

  • Inventory Linux kernel versions across hosts, guests, appliances, and embedded systems.
  • Check whether vsock support is present and exposed to local users or workloads.
  • Compare installed kernels against distro advisories and referenced stable commits.
  • Confirm patched systems boot the updated kernel after maintenance.
  • Monitor kernel logs for vsock warnings after patching.
Prepared
Confidence
high
Sources
11

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.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-476: Exact CWE lookup

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cve · low confidence lookup

CVE-2025-21666 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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
3ADP providers
10Source links

SSVC decision data

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

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
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

5.5Medium
CVSS 3.1 vector shape for CVE-2025-21666Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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
CVECVE Program Container
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxc0cfa2d8a788fcf45df5bf4070ab2474c88d543a, c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, c0cfa2d8a788fcf45df5bf4070ab2474c88d543aunaffected
LinuxLinux5.5, 0, 5.10.234, 5.15.177, 6.1.127, 6.6.74, 6.12.11, 6.13affected
Weakness

CWE details

CWE-476

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-476 · source CWE mapping

NULL Pointer Dereference

NULL Pointer Dereference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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