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NVD / CVE Program· CNA Linux

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

MediumCVSS 4.7 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 18/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.15% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. Special conditions such as timing or configuration are required.
  • Fixed version: Linux Linux 1063ae07383c0ddc5bcce170260c143825846b03, 9e79fdabd52cfce1a021640a81256878a2c516a2, d91bfc64a4886102746e74d2c6f3a61e9a77fd7d.
  • Severity is disputed: the assigning authority (CNA) scores it 7.8, NVD 4.7.

Low priority for now. Upgrade to Linux Linux 1063ae07383c0ddc5bcce170260c143825846b03, 9e79fdabd52cfce1a021640a81256878a2c516a2, d91bfc64a4886102746e74d2c6f3a61e9a77fd7d or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

Published
Apr 1, 2025
Updated
Aug 5, 2026
EPSS
0.1% · 4th percentile

Report tools

JSON

Action score

18

Monitor

Low priority for now.

CVSS
18 / 40 · 4.7 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CNA vs NVD score

NVD
4.7
CNA · Linux
7.8
3.1 point gap

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 6.12affected
    • fcb1aa5163b1ae4cf2864b688b08927aac51f51e and later · before 9e79fdabd52cfce1a021640a81256878a2c516a2affected · git
    • fcb1aa5163b1ae4cf2864b688b08927aac51f51e and later · before d91bfc64a4886102746e74d2c6f3a61e9a77fd7daffected · git
    • fcb1aa5163b1ae4cf2864b688b08927aac51f51e and later · before 1063ae07383c0ddc5bcce170260c143825846b03affected · git
    • before 6.12not affected · semver
    • 6.12.20 and later · up to and including 6.12.*not affected · semver
    • 6.13.8 and later · up to and including 6.13.*not affected · semver
    • 6.14 and laternot affected · original_commit_for_fix

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel6.12 and later · before 6.12.20
  • linux linux kernel6.13 and later · before 6.13.8
  • linux linux kernel6.14

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:13linuxbefore 6.12.20-16.12.20-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe…KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2025-21956Apr 1, 2025 · drm/amd/display: Assign normalized_pix_clk when color depth = 14
    22Monitor
  • ← EarlierCVE-2025-21957Apr 1, 2025 · scsi: qla1280: Fix kernel oops when debug level > 2
    22Monitor
  • Later →CVE-2025-21960Apr 1, 2025 · eth: bnxt: do not update checksum in bnxt_xdp_build_skb()
    22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux1063ae07383c0ddc5bcce170260c143825846b03Vendor (CNA)
Linux Linux9e79fdabd52cfce1a021640a81256878a2c516a2Vendor (CNA)
Linux Linuxd91bfc64a4886102746e74d2c6f3a61e9a77fd7dVendor (CNA)
debian:linux6.12.20-1 · Debian:13Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2025-38352112 days apartposix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del()KEV
    61This week
  • CVE-2026-64091474 days apartbatman-adv: tt: fix TOCTOU race for reported vlans
    39Monitor
  • CVE-2026-64034474 days apartnet: mana: Fix TOCTOU double-fetch of hwc_msg_id from DMA buffer
    37Monitor
  • CVE-2026-63937474 days apartKVM: SEV: Use READ_ONCE() when reading entries/indices from PSC buffer
    35Monitor
  • CVE-2026-63867474 days apartmptcp: close TOCTOU race while computing rcv_wnd
    32Monitor
  • CVE-2026-31678389 days apartopenvswitch: defer tunnel netdev_put to RCU release
    31Monitor

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · public bounty program.

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-367 · Time-of-check Time-of-use (TOCTOU) Race Condition

CVSS vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

References

Show all references (2 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records