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CVE Record

CVE-2025-40173: net/ip6_tunnel: Prevent perpetual tunnel growth

In the Linux kernel, the following vulnerability has been resolved: net/ip6_tunnel: Prevent perpetual tunnel growth Similarly to ipv4 tunnel, ipv6 version updates dev->needed_headroom, too. While ipv4 tunnel headroom adjustment growth was limited in commit 5ae1e9922bbd ("net: ip_tunnel: prevent perpetual headroom growth"), ipv6 tunnel yet increases the headroom without any ceiling. Reflect ipv4 tunnel headroom adjustment limit on ipv6 version. Credits to Francesco Ruggeri, who was originally debugging this issue and wrote local Arista-specific patch and a reproducer.

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 IPv6 tunneling flaw lets a network-device headroom value grow without a defined ceiling. The supplied CVSS score is 7.8 (high) and models local, low-privileged access, making this primarily a post-access host risk rather than an unauthenticated internet threat. Affected systems should receive vendor-backed kernel updates.

Executive priority

Treat this as high priority, but not an internet-wide emergency based on current evidence. Expedite patching on shared, multi-user, or otherwise locally exposed Linux hosts. Handle isolated systems through the normal high-severity kernel cycle, escalating if vendor guidance or new exploitation evidence changes the local-access assumptions.

Technical view

The IPv6 tunnel path updates dev->needed_headroom without the ceiling already implemented for IPv4 tunneling. The fix applies the IPv4-style adjustment limit to IPv6. The CVSS vector is AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. The bundle does not explain how unbounded growth produces the scored confidentiality, integrity, and availability impacts.

Likely exposure

Likely exposure is Linux systems running affected kernel builds where IPv6 tunnel behavior can be exercised. The record names versions from 4.7 and several stable-series builds through 6.18, but lacks sufficient distribution-package mapping and configuration prerequisites to determine vulnerability solely from a version string.

Exploitation context

The supplied bundle marks KEV as false and cites no active exploitation or public weaponization. The CVSS vector describes local, low-complexity exploitation requiring low privileges and no user interaction. KEV absence is not proof exploitation has never occurred; current evidence supports treating this as a local or post-access risk.

Researcher notes

The patch mirrors the IPv4 ceiling from commit 5ae1e9922bbd in net/ip6_tunnel. Multiple stable references indicate branch-specific fixes. A reproducer is credited, but none is included in the supplied evidence. Exact trigger conditions, affected distribution packages, observable indicators, and real-world exploitation remain unconfirmed here.

Mitigation direction

  • Apply the Linux distribution or appliance vendor's kernel update containing the appropriate referenced stable fix.
  • Reboot into the updated kernel and retire the vulnerable running build.
  • Where updates are unavailable, request vendor guidance; the supplied sources name no verified workaround.
  • Reduce unnecessary local account access on affected shared systems until remediation is complete.

Validation and detection

  • Inventory running kernel builds and identify systems using IPv6 tunnel functionality.
  • Map each vendor build to its advisory or backport of a referenced stable commit.
  • After reboot, confirm the running kernel is the remediated build, not merely an installed package.
  • Document and reassess deferred systems, especially those accessible to untrusted local users or workloads.
Prepared
Confidence
medium
Sources
10

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-2025-40173 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
9Source 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-2025-40173Attack 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
LinuxLinux8eb30be0352d09165e94a41fef1c7b994dca0714, 8eb30be0352d09165e94a41fef1c7b994dca0714, 8eb30be0352d09165e94a41fef1c7b994dca0714, 8eb30be0352d09165e94a41fef1c7b994dca0714, 8eb30be0352d09165e94a41fef1c7b994dca0714, 8eb30be0352d09165e94a41fef1c7b994dca0714, 8eb30be0352d09165e94a41fef1c7b994dca0714, 8eb30be0352d09165e94a41fef1c7b994dca0714unaffected
LinuxLinux4.7, 0, 5.4.301, 5.10.246, 5.15.196, 6.1.158, 6.6.114, 6.12.55, 6.17.5, 6.18affected
Weakness

CWE details

No CWE listed

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