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CVE Record

CVE-2025-21764: ndisc: use RCU protection in ndisc_alloc_skb()

In the Linux kernel, the following vulnerability has been resolved: ndisc: use RCU protection in ndisc_alloc_skb() ndisc_alloc_skb() can be called without RTNL or RCU being held. Add RCU protection to avoid possible UAF.

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 IPv6 Neighbor Discovery memory-safety flaw may let a local user with limited privileges compromise an affected system’s confidentiality, integrity, or availability. The risk is significant, but the supplied sources provide no evidence of active exploitation or a working public exploit. Organizations should prioritize vendor-supported kernel updates based on local-user exposure and system criticality.

Executive priority

Treat this as a high-priority kernel update for systems where untrusted or lower-privileged users can execute locally. Accelerate remediation on shared and critical hosts. Internet-facing status alone should not determine priority because the documented attack vector is local. Use normal expedited patching rather than emergency incident response unless monitoring or vendor intelligence reveals exploitation.

Technical view

ndisc_alloc_skb() may execute without RTNL or RCU protection, creating a possible use-after-free condition in Linux IPv6 Neighbor Discovery code. Upstream stable fixes add RCU protection. CVE-2025-21764 is CWE-416 with CVSS 3.1 score 7.8: local access, low privileges, low complexity, no user interaction, and potentially high confidentiality, integrity, and availability impact.

Likely exposure

Exposure is limited to systems running an affected Linux kernel without an upstream fix or downstream backport. The CVSS vector indicates local access and low privileges, so network reachability alone does not establish exposure. The bundled version data is flattened; confirm exact affected and fixed package versions through the applicable Linux distribution or appliance vendor.

Exploitation context

CISA KEV status is false, and the supplied sources do not report active exploitation. The CVSS assessment indicates a low-privileged local attacker may reach the vulnerable condition, but the bundle does not establish practical exploitation reliability, required configuration, or whether IPv6 must be operational. Absence from KEV is not proof that exploitation cannot occur.

Researcher notes

The defect concerns missing synchronization around ndisc_alloc_skb(), with upstream commits adding RCU protection to prevent a possible use-after-free. Multiple stable-branch commits and Debian advisories indicate backport activity. The supplied evidence does not describe a reproducer, exploitation primitive, affected runtime configurations, or confirmed attacks. Exact branch boundaries should be taken from the full CVE record and vendor packaging metadata.

Mitigation direction

  • Install a vendor-supported kernel containing the applicable upstream fix or downstream backport.
  • Use distribution or appliance advisories to identify the correct fixed package version.
  • Prioritize multi-user, shared-hosting, container-host, and other systems granting untrusted local access.
  • Reboot into the updated kernel after installation, following operational change controls.
  • If updates are delayed, review vendor guidance for supported temporary mitigations.

Validation and detection

  • Record each system’s running kernel version and distribution package release.
  • Compare versions against the applicable vendor advisory, including documented backports.
  • Confirm the running kernel changed after remediation, not merely the installed package.
  • Verify the vendor patch maps to an upstream stable fix referenced by this CVE.
  • Retest critical IPv6 networking functions after updating the kernel.
Prepared
Confidence
medium
Sources
12

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-416: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2025-21764 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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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
3ADP providers
13Source links

SSVC decision data

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

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

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2025-21764Attack 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
CVECVE Program Container
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxde09334b9326632bbf1a74bfd8b01866cbbf2f61, de09334b9326632bbf1a74bfd8b01866cbbf2f61, de09334b9326632bbf1a74bfd8b01866cbbf2f61, de09334b9326632bbf1a74bfd8b01866cbbf2f61, de09334b9326632bbf1a74bfd8b01866cbbf2f61, de09334b9326632bbf1a74bfd8b01866cbbf2f61, de09334b9326632bbf1a74bfd8b01866cbbf2f61, de09334b9326632bbf1a74bfd8b01866cbbf2f61unaffected
LinuxLinux3.9, 0, 5.4.291, 5.10.235, 5.15.179, 6.1.129, 6.6.79, 6.12.16, 6.13.4, 6.14affected
Weakness

CWE details

CWE-416

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

CWE-416 · source CWE mapping

Use After Free

Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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