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CVE Record

CVE-2026-23209: macvlan: fix error recovery in macvlan_common_newlink()

In the Linux kernel, the following vulnerability has been resolved: macvlan: fix error recovery in macvlan_common_newlink() valis provided a nice repro to crash the kernel: ip link add p1 type veth peer p2 ip link set address 00:00:00:00:00:20 dev p1 ip link set up dev p1 ip link set up dev p2 ip link add mv0 link p2 type macvlan mode source ip link add invalid% link p2 type macvlan mode source macaddr add 00:00:00:00:00:20 ping -c1 -I p1 1.2.3.4 He also gave a very detailed analysis: <quote valis> The issue is triggered when a new macvlan link is created with MACVLAN_MODE_SOURCE mode and MACVLAN_MACADDR_ADD (or MACVLAN_MACADDR_SET) parameter, lower device already has a macvlan port and register_netdevice() called from macvlan_common_newlink() fails (e.g. because of the invalid link name). In this case macvlan_hash_add_source is called from macvlan_change_sources() / macvlan_common_newlink(): This adds a reference to vlan to the port's vlan_source_hash using macvlan_source_entry. vlan is a pointer to the priv data of the link that is being created. When register_netdevice() fails, the error is returned from macvlan_newlink() to rtnl_newlink_create(): if (ops->newlink) err = ops->newlink(dev, &params, extack); else err = register_netdevice(dev); if (err < 0) { free_netdev(dev); goto out; } and free_netdev() is called, causing a kvfree() on the struct net_device that is still referenced in the source entry attached to the lower device's macvlan port. Now all packets sent on the macvlan port with a matching source mac address will trigger a use-after-free in macvlan_forward_source(). </quote valis> With all that, my fix is to make sure we call macvlan_flush_sources() regardless of @create value whenever "goto destroy_macvlan_port;" path is taken. Many thanks to valis for following up on this issue.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel memory-safety flaw in macvlan networking. A local user who can create specific macvlan interfaces can leave the kernel referencing freed memory, and later traffic can crash or potentially compromise the system. It is high severity, but the provided sources do not show active exploitation.

Executive priority

Treat as a high-priority kernel update for shared Linux infrastructure and container hosts. The issue requires local capability, so urgency is highest where users or workloads can administer networking. No cited source shows active exploitation, but impact is severe if reachable.

Technical view

The bug is in macvlan_common_newlink() error recovery. When source-mode macvlan creation with MACVLAN_MACADDR_ADD or SET fails during register_netdevice(), a source-hash entry can keep a pointer to freed net_device private data. Matching packets then reach macvlan_forward_source() and trigger use-after-free.

Likely exposure

Exposure is most relevant on Linux hosts where local users, containers, automation, or tenants can create macvlan links or hold network-administration privileges. Systems not using macvlan may still be vulnerable if the affected kernel code is present, but practical reach depends on local permission boundaries.

Exploitation context

The CVSS vector is local, low complexity, low privileges, no user interaction, with high confidentiality, integrity, and availability impact. The bundle marks KEV as false and provides no evidence of exploitation in the wild.

Researcher notes

The root cause is incomplete cleanup on the destroy_macvlan_port path after failed newlink registration. The fix calls macvlan_flush_sources() regardless of the create value. Evidence is strong for the bug and fix, but affected distribution package status is not provided in the bundle.

Mitigation direction

  • Apply a fixed Linux stable or distribution kernel containing the referenced macvlan fixes.
  • Check distribution advisories for backported package names and fixed kernel builds.
  • Restrict untrusted users and containers from creating macvlan interfaces until patched.
  • Review CAP_NET_ADMIN and network namespace permissions on multi-tenant Linux hosts.
  • Avoid source-mode macvlan creation in untrusted workflows until remediation is confirmed.

Validation and detection

  • Inventory Linux kernel versions across hosts and images.
  • Confirm whether the relevant stable fix commit is present or backported.
  • Identify systems using macvlan, especially source mode.
  • Audit containers, CI jobs, and users with network-administration capability.
  • Prioritize validation on shared, containerized, or tenant-accessible hosts.
Prepared
Confidence
high
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

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CVE-2026-23209 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
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
7.8CVSS 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-2026-23209Attack 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
LinuxLinuxaa5fd0fb77486b8a6764ead8627baa14790e4280, aa5fd0fb77486b8a6764ead8627baa14790e4280, aa5fd0fb77486b8a6764ead8627baa14790e4280, aa5fd0fb77486b8a6764ead8627baa14790e4280, aa5fd0fb77486b8a6764ead8627baa14790e4280, aa5fd0fb77486b8a6764ead8627baa14790e4280, aa5fd0fb77486b8a6764ead8627baa14790e4280unaffected
LinuxLinux4.9, 0, 5.10.250, 5.15.200, 6.1.163, 6.6.124, 6.12.70, 6.18.10, 6.19affected
Weakness

CWE details

No CWE listed

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