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CVE Record

CVE-2026-23139: netfilter: nf_conncount: update last_gc only when GC has been performed

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conncount: update last_gc only when GC has been performed Currently last_gc is being updated everytime a new connection is tracked, that means that it is updated even if a GC wasn't performed. With a sufficiently high packet rate, it is possible to always bypass the GC, causing the list to grow infinitely. Update the last_gc value only when a GC has been actually performed.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-23139 is a Linux kernel availability flaw in netfilter connection counting. Under sufficiently high packet rates, cleanup can be skipped and internal tracking lists can grow without bound. The business risk is denial of service on affected Linux systems, especially systems using netfilter connection-counting controls on exposed network paths.

Executive priority

Treat as high priority for Linux infrastructure on network edges or enforcing connection limits. It is an availability risk with no cited active exploitation, so prioritize patching based on exposure rather than emergency-wide disruption.

Technical view

The issue is in nf_conncount. The kernel updated last_gc whenever a new connection was tracked, even when garbage collection did not run. High packet rate can keep bypassing garbage collection, allowing unbounded list growth. The resolved behavior updates last_gc only after garbage collection is actually performed.

Likely exposure

Exposure is most relevant to affected Linux kernels using netfilter nf_conncount or related connection-limit rules. Internet-facing firewalls, gateways, load balancers, and hosts enforcing connection-count policies should be prioritized. The provided source bundle does not identify affected distributions or appliances.

Exploitation context

The CVE record scores this as network-reachable, low-complexity, unauthenticated, and high availability impact. The source bundle does not report active exploitation, and KEV status is false. The documented trigger is sufficiently high packet rate causing garbage collection bypass and list growth.

Researcher notes

The source evidence is limited to the CVE description and upstream stable commit references. Affected version data in the bundle is not distribution-specific. Researchers should map upstream fixes to deployed kernel builds and avoid assuming exposure without nf_conncount usage evidence.

Mitigation direction

  • Apply Linux kernel updates containing the referenced stable fixes.
  • Check distribution or appliance vendor advisories for packaged kernel availability.
  • Prioritize exposed systems using netfilter connection-counting features.
  • Use compensating traffic controls where patching is delayed.
  • Monitor memory pressure and connection-tracking behavior until updated.

Validation and detection

  • Inventory Linux kernel versions on exposed systems.
  • Identify hosts using netfilter nf_conncount or connection-limit rules.
  • Confirm vendor kernel packages include the referenced upstream fixes.
  • Review monitoring for abnormal memory growth under network load.
  • Track whether vendor advisories expand affected version guidance.
Prepared
Confidence
medium
Sources
9

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-2026-23139 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/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
0ADP providers
8Source 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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-23139Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/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.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxf106694733c66a48740c25bc4e212e9b2ea364ce, be69850b461e7b491d87a22e33ab76fdd04b725e, d265929930e2ffafc744c0ae05fb70acd53be1ee, d265929930e2ffafc744c0ae05fb70acd53be1ee, d265929930e2ffafc744c0ae05fb70acd53be1ee, d265929930e2ffafc744c0ae05fb70acd53be1ee, d265929930e2ffafc744c0ae05fb70acd53be1eeunaffected
LinuxLinux5.19, 0, 6.1.161, 6.6.121, 6.12.66, 6.18.6, 6.19affected
Weakness

CWE details

No CWE listed

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