CVE-2025-39843

Local denial of service via recursive timer lock

Published Sep 19, 2025 · Updated Sep 19, 2025

Deadlock in the Linux kernel allows local users to hang debug builds under rare timing conditions during high-resolution timer activation. set_track_prepare can wake kswapd while hrtimer_start_range_ns holds the same per-CPU timer-base lock, causing recursive lock acquisition. Exploitation requires a debug kernel with timer-object, SLUB-debug, stack-depot, and user-allocation tracking features enabled; standard production kernels are not triggerable.

CVSS severity5.5
Medium
EPSS probability0.11%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Deadlock in the Linux kernel allows local users to hang debug builds under rare timing conditions during high-resolution timer activation. set_track_prepare can wake kswapd while hrtimer_start_range_ns holds the same per-CPU timer-base lock, causing recursive lock acquisition. Exploitation requires a debug kernel with timer-object, SLUB-debug, stack-depot, and user-allocation tracking features enabled; standard production kernels are not triggerable.

The record

CVE
CVE-2025-39843
Published
Sep 19, 2025
Updated
Sep 19, 2025
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-833, CWE-667, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 19, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 19, 2025Record 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=5.19
  2. Affected versionversion=5cf909c553e9efed573811de4b3f5172898d5515 <243b705a90ed8449f561a271cf251fd2e939f3db
  3. Affected versionversion=5cf909c553e9efed573811de4b3f5172898d5515 <522ffe298627cfe72539d72167c2e20e72b5e856
  4. Affected versionversion=5cf909c553e9efed573811de4b3f5172898d5515 <850470a8413a8a78e772c4f6bd9fe81ec6bd5b0f
  5. Affected versionversion=5cf909c553e9efed573811de4b3f5172898d5515 <994b03b9605d36d814c611385fbf90ca6db20aa8
  6. Affected versionversion=5cf909c553e9efed573811de4b3f5172898d5515 <eb3240ffd243bfb8b1e9dc568d484ecf9fd660ab

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.19; version=5cf909c553e9efed573811de4b3f5172898d5515 <243b705a90ed8449f561a271cf251fd2e939f3db; version=5cf909c553e9efed573811de4b3f5172898d5515 <522ffe298627cfe72539d72167c2e20e72b5e856; version=5cf909c553e9efed573811de4b3f5172898d5515 <850470a8413a8a78e772c4f6bd9fe81ec6bd5b0f; version=5cf909c553e9efed573811de4b3f5172898d5515 <994b03b9605d36d814c611385fbf90ca6db20aa8; version=5cf909c553e9efed573811de4b3f5172898d5515 <eb3240ffd243bfb8b1e9dc568d484ecf9fd660ab

Published CVSS scores

4.7Red HatCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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-833Deadlock
CWE-667Improper Locking
T1499.004Application or System Exploitation

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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