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CVE Record

CVE-2025-21758: ipv6: mcast: add RCU protection to mld_newpack()

In the Linux kernel, the following vulnerability has been resolved: ipv6: mcast: add RCU protection to mld_newpack() mld_newpack() can be called without RTNL or RCU being held. Note that we no longer can use sock_alloc_send_skb() because ipv6.igmp_sk uses GFP_KERNEL allocations which can sleep. Instead use alloc_skb() and charge the net->ipv6.igmp_sk socket under RCU protection.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2025-21758 is a Linux kernel IPv6 multicast bug. The public description says a kernel function can run without required locking protection, creating a concurrency-safety issue. Severity is not scored in the provided record, so business urgency depends on where affected Linux kernels are used, especially internet, network, or appliance workloads with IPv6 enabled.

Executive priority

Prioritize normal security patching unless vendor advisories identify critical affected assets. Escalate for internet-facing, network infrastructure, industrial, or appliance systems because kernel issues can have high operational impact even when severity metadata is incomplete.

Technical view

The issue is in IPv6 multicast handling: mld_newpack() may be called without RTNL or RCU held. The kernel fix adds RCU protection and changes allocation behavior around net->ipv6.igmp_sk charging. The source bundle does not provide CVSS, CWE, privilege requirements, or a confirmed impact class.

Likely exposure

Exposure is likely limited to Linux systems running affected kernel builds with IPv6 multicast code reachable. The bundle also references Debian LTS and Siemens advisories, suggesting downstream products or distributions may include affected kernels. Exact affected product versions beyond the provided Linux kernel entries require vendor confirmation.

Exploitation context

The bundle does not report active exploitation, public exploit code, or CISA KEV listing. Treat exploitation status as unconfirmed. The available evidence supports a kernel concurrency flaw fixed upstream, not a demonstrated attack path.

Researcher notes

The public record is sparse: no CVSS, CWE, impact statement, or exploitability details are provided. Analysis should focus on code-path reachability, kernel branch mapping, and downstream vendor advisories. Avoid assuming privilege level, remote exploitability, or denial-of-service impact without additional source evidence.

Mitigation direction

  • Update Linux kernels through distribution or vendor-supported security channels.
  • Prioritize systems using IPv6, network appliances, and externally exposed Linux hosts.
  • Review Debian LTS guidance if running Debian LTS kernels.
  • Review Siemens advisories for affected industrial or appliance products.
  • Track kernel stable fixes referenced in the CVE record.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and embedded systems.
  • Confirm whether IPv6 is enabled on potentially affected systems.
  • Map installed kernels against vendor advisories and fixed package releases.
  • Check Debian LTS or product vendor bulletins for applicable updates.
  • Document exceptions where vendor-fixed kernels are not yet available.
Prepared
Confidence
medium
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

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CVE-2025-21758 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
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.

0CVSS vectors
3Timeline events
2ADP providers
10Source links

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

CVECVE Program Container
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxb8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551, b8ad0cbc58f703972e9e37c4e2a8081dd7e6a551unaffected
LinuxLinux2.6.26, 0, 5.15.179, 6.1.129, 6.6.79, 6.12.16, 6.13.4, 6.14affected
Weakness

CWE details

No CWE listed

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