CVE-2025-21958

Kernel memory corruption via conntrack extension reallocation

Published Apr 1, 2025 · Updated Aug 5, 2026

Use-after-free in Linux kernel Open vSwitch conntrack allows local users to disclose or corrupt kernel memory and crash the host. ovs_ct_get_conn_labels() calls nf_ct_ext_add() to reallocate ct->ext after the conntrack entry is confirmed and visible to lock-free readers, creating use-after-free reads and writes. Local users can obtain CAP_NET_ADMIN in a user namespace, order conntrack creation and a labeled OVS flow, and use concurrent traffic to disclose kernel heap data, corrupt memory, or panic the host.

CVSS severity7.8
High
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in Linux kernel Open vSwitch conntrack allows local users to disclose or corrupt kernel memory and crash the host. ovs_ct_get_conn_labels() calls nf_ct_ext_add() to reallocate ct->ext after the conntrack entry is confirmed and visible to lock-free readers, creating use-after-free reads and writes. Local users can obtain CAP_NET_ADMIN in a user namespace, order conntrack creation and a labeled OVS flow, and use concurrent traffic to disclose kernel heap data, corrupt memory, or panic the host.

The record

CVE
CVE-2025-21958
Published
Apr 1, 2025
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499.004, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 1, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=6.12
  2. Affected versionversion=fcb1aa5163b1ae4cf2864b688b08927aac51f51e <1063ae07383c0ddc5bcce170260c143825846b03
  3. Affected versionversion=fcb1aa5163b1ae4cf2864b688b08927aac51f51e <9e79fdabd52cfce1a021640a81256878a2c516a2
  4. Affected versionversion=fcb1aa5163b1ae4cf2864b688b08927aac51f51e <d91bfc64a4886102746e74d2c6f3a61e9a77fd7d

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=6.12; version=fcb1aa5163b1ae4cf2864b688b08927aac51f51e <1063ae07383c0ddc5bcce170260c143825846b03; version=fcb1aa5163b1ae4cf2864b688b08927aac51f51e <9e79fdabd52cfce1a021640a81256878a2c516a2; version=fcb1aa5163b1ae4cf2864b688b08927aac51f51e <d91bfc64a4886102746e74d2c6f3a61e9a77fd7d

Published CVSS scores

4.7UbuntuCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
7.8Linux CNACVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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