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CVE Record

CVE-2025-21958: Revert "openvswitch: switch to per-action label counting in conntrack"

In the Linux kernel, the following vulnerability has been resolved: Revert "openvswitch: switch to per-action label counting in conntrack" Currently, ovs_ct_set_labels() is only called for confirmed conntrack entries (ct) within ovs_ct_commit(). However, if the conntrack entry does not have the labels_ext extension, attempting to allocate it in ovs_ct_get_conn_labels() for a confirmed entry triggers a warning in nf_ct_ext_add(): WARN_ON(nf_ct_is_confirmed(ct)); This happens when the conntrack entry is created externally before OVS increments net->ct.labels_used. The issue has become more likely since commit fcb1aa5163b1 ("openvswitch: switch to per-action label counting in conntrack"), which changed to use per-action label counting and increment net->ct.labels_used when a flow with ct action is added. Since there’s no straightforward way to fully resolve this issue at the moment, this reverts the commit to avoid breaking existing use cases.

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 Open vSwitch conntrack change can mishandle connection labels when another component created the connection-tracking entry first. This can trigger a kernel warning and disrupt established networking use cases. The supplied CVSS score is 7.8, reflecting potentially serious local impact under the scored threat model.

Executive priority

Prioritize remediation on network infrastructure, virtualization hosts, and container platforms that actively use Open vSwitch conntrack. Other Linux systems should first be inventoried for OVS usage. The high score warrants timely action, but the supplied evidence does not support declaring an active exploitation emergency.

Technical view

The per-action label-counting change can let OVS process a confirmed conntrack entry without the labels_ext extension. Adding that extension after confirmation triggers WARN_ON in nf_ct_ext_add(). The kernel resolution reverts the responsible change because no straightforward complete fix was available. Exploitation requires local access according to the supplied CVSS vector.

Likely exposure

Exposure is concentrated on affected Linux kernels running Open vSwitch with conntrack actions, particularly where conntrack entries may be created externally before OVS updates label accounting. The bundle identifies Linux 6.12, 6.12.20, 6.13.8, and 6.14, but its version data is ambiguous; confirm exact vendor build status.

Exploitation context

The supplied CVSS vector indicates local, low-complexity exploitation requiring low privileges and no user interaction. The source bundle marks KEV false and provides no evidence of active exploitation or a public exploit. Practical exploitability beyond triggering the documented warning is not established here.

Researcher notes

The triggering state requires a confirmed conntrack entry created before OVS increments net->ct.labels_used, leaving labels_ext absent when ovs_ct_set_labels() runs. The documented resolution is a revert, suggesting regression avoidance rather than a redesigned label-allocation mechanism. The bundle does not establish reliable code execution or observed real-world attacks.

Mitigation direction

  • Update to a vendor-supported kernel containing the applicable referenced stable revert.
  • Prioritize hosts using Open vSwitch conntrack actions or connection labels.
  • If immediate updating is impossible, consult vendor guidance before changing OVS conntrack behavior.
  • Do not treat unverified configuration workarounds as complete remediation.

Validation and detection

  • Inventory kernel versions and map vendor builds to the affected ranges and referenced stable fixes.
  • Confirm whether Open vSwitch conntrack actions and connection labels are used.
  • Review kernel logs for nf_ct_ext_add warnings involving confirmed conntrack entries.
  • After updating, rerun representative OVS traffic tests and confirm warnings do not recur.
Prepared
Confidence
medium
Sources
5

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

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CVE-2025-21958 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
4Source 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-2025-21958Attack 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
LinuxLinuxfcb1aa5163b1ae4cf2864b688b08927aac51f51e, fcb1aa5163b1ae4cf2864b688b08927aac51f51e, fcb1aa5163b1ae4cf2864b688b08927aac51f51eunaffected
LinuxLinux6.12, 0, 6.12.20, 6.13.8, 6.14affected
Weakness

CWE details

No CWE listed

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