CVE-2025-21839

Guest hang via stale DR6 reload

Published Mar 7, 2025 · Updated Aug 5, 2026

Improper initialization in Linux KVM allows local users to corrupt guest DR6 state through a fastpath VM-Exit on x86 hosts. The VMX and SVM vCPU run loops reload hardware DR6 from stale vcpu->arch.dr6 data before common VM-Exit code saves the guest's current value. Reaching the flaw requires KVM guest execution or local /dev/kvm access; corrupted trap bits can conceal breakpoint hits, hang a vCPU, or panic a guest configured with panic_on_warn.

CVSS severity7.3
High
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper initialization in Linux KVM allows local users to corrupt guest DR6 state through a fastpath VM-Exit on x86 hosts. The VMX and SVM vCPU run loops reload hardware DR6 from stale vcpu->arch.dr6 data before common VM-Exit code saves the guest's current value. Reaching the flaw requires KVM guest execution or local /dev/kvm access; corrupted trap bits can conceal breakpoint hits, hang a vCPU, or panic a guest configured with panic_on_warn.

The record

CVE
CVE-2025-21839
Published
Mar 7, 2025
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-665, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 7, 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

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Is a vulnerable build present?

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

  1. Affected versionversion=5.7
  2. Affected versionversion=d67668e9dd76d98136048935723947156737932b <4eb063de686bfcdfd03a8c801d1bbe87d2d5eb55
  3. Affected versionversion=d67668e9dd76d98136048935723947156737932b <93eeb6df1605b3a24f38afdba7ab903ba6b64133
  4. Affected versionversion=d67668e9dd76d98136048935723947156737932b <9efb2b99b96c86664bbdbdd2cdb354ac9627eb20
  5. Affected versionversion=d67668e9dd76d98136048935723947156737932b <a1723e9c53fe6431415be19302a56543daf503f5
  6. Affected versionversion=d67668e9dd76d98136048935723947156737932b <c2fee09fc167c74a64adb08656cb993ea475197e
  7. Affected versionversion=d67668e9dd76d98136048935723947156737932b <d456de38d9eb753a4e9fde053c18d4ef8e485339

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.7; version=d67668e9dd76d98136048935723947156737932b <4eb063de686bfcdfd03a8c801d1bbe87d2d5eb55; version=d67668e9dd76d98136048935723947156737932b <93eeb6df1605b3a24f38afdba7ab903ba6b64133; version=d67668e9dd76d98136048935723947156737932b <9efb2b99b96c86664bbdbdd2cdb354ac9627eb20; version=d67668e9dd76d98136048935723947156737932b <a1723e9c53fe6431415be19302a56543daf503f5; version=d67668e9dd76d98136048935723947156737932b <c2fee09fc167c74a64adb08656cb993ea475197e; version=d67668e9dd76d98136048935723947156737932b <d456de38d9eb753a4e9fde053c18d4ef8e485339

Published CVSS scores

7.3LinuxCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:L/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-665Improper Initialization
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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