Local privilege escalation via cls_u32 reference undercount
Published Sep 6, 2023 · Updated Feb 13, 2025
Use-after-free in the Linux Kernel cls_u32 classifier before 6.5 allows local users to gain root privileges through crafted traffic-control filters. u32_change copies the existing tcf_result, then tcf_unbind_filter decrements the referenced class count so the class can be freed while an active filter still points to it. The demonstrated chain requires local code execution and traffic-control access; reclaiming the freed object enables kernel control-flow hijacking and root-level command execution.
Summary
What happened
Use-after-free in the Linux Kernel cls_u32 classifier before 6.5 allows local users to gain root privileges through crafted traffic-control filters. u32_change copies the existing tcf_result, then tcf_unbind_filter decrements the referenced class count so the class can be freed while an active filter still points to it. The demonstrated chain requires local code execution and traffic-control access; reclaiming the freed object enables kernel control-flow hijacking and root-level command execution.
The record
- CVE
- CVE-2023-4208
- Published
- Sep 6, 2023
- Updated
- Feb 13, 2025
- Vendor
- The Linux Kernel Organization
- Product
- Linux Kernel
- Classifications
- CWE-416, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Sep 6, 2023CVE publishedPublication date reported by the CVE source.
- Feb 13, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=3.18 <6.5
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
- Google security-research KernelCTF exploitfunctional · demonstrated
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Technologies
Your stack
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Your stack
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