CVE-2023-3609

Local privilege escalation via cls_u32 reference rollover

Published Jul 21, 2023 · Updated Jul 30, 2026

Use-after-free in the cls_u32 traffic-control classifier in Linux Kernel allows local users to gain root privileges. Repeated tcf_change_indev() failures leave tcf_bind_filter() reference increments unwound until counter rollover frees a still-referenced object. Exploitation requires local low-privileged access and unprivileged user namespaces; successful memory corruption grants kernel-level control and can crash the host.

CVSS severity7.8
High
EPSS probability0.45%
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 the cls_u32 traffic-control classifier in Linux Kernel allows local users to gain root privileges. Repeated tcf_change_indev() failures leave tcf_bind_filter() reference increments unwound until counter rollover frees a still-referenced object. Exploitation requires local low-privileged access and unprivileged user namespaces; successful memory corruption grants kernel-level control and can crash the host.

The record

CVE
CVE-2023-3609
Published
Jul 21, 2023
Updated
Jul 30, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-416, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 21, 2023CVE publishedPublication date reported by the CVE source.
  2. Jul 30, 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=4.14.0 <4.14.322
  2. Affected versionversion=4.15.0 <4.19.291
  3. Affected versionversion=4.20.0 <5.4.248
  4. Affected versionversion=5.11.0 <5.15.118
  5. Affected versionversion=5.16.0 <6.1.35
  6. Affected versionversion=5.5.0 <5.10.185
  7. Affected versionversion=6.2.0 <6.3.9

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=4.14.0 <4.14.322; version=4.15.0 <4.19.291; version=4.20.0 <5.4.248; version=5.11.0 <5.15.118; version=5.16.0 <6.1.35; version=5.5.0 <5.10.185; version=6.2.0 <6.3.9

Published CVSS scores

7.8Canonical UbuntuCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8Google LLCCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.0Oracle LinuxCVSS:3.0/AV:L/AC:H/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

CWE-416Use After Free
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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