Kernel panic via uninitialized IDLETIMER timer type
Published May 22, 2024 · Updated Aug 5, 2026
Denial of service in the Linux kernel allows local users to trigger a kernel panic through xt_IDLETIMER timer sysfs reads. idletimer_tg_create allocates the timer with kmalloc but leaves timer_type uninitialized, so idletimer_tg_show can treat residual memory as a valid timer type and dereference an invalid alarm timer. Exploitation requires an IDLETIMER rule created through the affected path; reading its timer entry can crash the entire host.
Summary
What happened
Denial of service in the Linux kernel allows local users to trigger a kernel panic through xt_IDLETIMER timer sysfs reads. idletimer_tg_create allocates the timer with kmalloc but leaves timer_type uninitialized, so idletimer_tg_show can treat residual memory as a valid timer type and dereference an invalid alarm timer. Exploitation requires an IDLETIMER rule created through the affected path; reading its timer entry can crash the entire host.
The record
- CVE
- CVE-2021-47451
- Published
- May 22, 2024
- Updated
- Aug 5, 2026
- Vendor
- The Linux Kernel Organization
- Product
- Linux
- Classifications
- CWE-908, T1499.004
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- May 22, 2024CVE publishedPublication date reported by the CVE source.
- Aug 5, 2026Record 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=5.7
- Affected versionversion=68983a354a655c35d3fb204489d383a2a051fda7 <2a670c323055282c9b72794a491d53cef86bbeaf
- Affected versionversion=68983a354a655c35d3fb204489d383a2a051fda7 <902c0b1887522a099aa4e1e6b4b476c2fe5dd13e
- Affected versionversion=68983a354a655c35d3fb204489d383a2a051fda7 <cae7cab804c943d723d52724a3aeb07a3f4a2650
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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