CVE-2026-63804

System crash via GFS2 unmount use-after-free

Published Jul 19, 2026 · Updated Jul 19, 2026

Use-after-free in the Linux Kernel GFS2 filesystem allows local users to crash affected systems during unmount operations. The gfs2_qd_dealloc RCU callback dereferences qd->qd_sbd after gfs2_put_super frees the superblock, so pending quota callbacks access released memory. Reachability requires local access, a GFS2 unmount, and either a quota-cleanup timeout or callbacks queued after its wait; the bounded impact is a system crash.

CVSS severity7.8
High
EPSS probability0.14%
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 Linux Kernel GFS2 filesystem allows local users to crash affected systems during unmount operations. The gfs2_qd_dealloc RCU callback dereferences qd->qd_sbd after gfs2_put_super frees the superblock, so pending quota callbacks access released memory. Reachability requires local access, a GFS2 unmount, and either a quota-cleanup timeout or callbacks queued after its wait; the bounded impact is a system crash.

The record

CVE
CVE-2026-63804
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-416, CWE-825, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 19, 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=6.6
  2. Affected versionversion=a475c5dd16e57c570113eccba51955b5df8bb052 <4fe388218826df8607ae41a6305df67db08a9093
  3. Affected versionversion=a475c5dd16e57c570113eccba51955b5df8bb052 <8745d9f7e1682c39f0a1578895ac74205e2a6757
  4. Affected versionversion=a475c5dd16e57c570113eccba51955b5df8bb052 <9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0
  5. Affected versionversion=a475c5dd16e57c570113eccba51955b5df8bb052 <b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0
  6. Affected versionversion=a475c5dd16e57c570113eccba51955b5df8bb052 <f9c9ec2c319f843b70ecdf939d48b52d189bc081

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=6.6; version=a475c5dd16e57c570113eccba51955b5df8bb052 <4fe388218826df8607ae41a6305df67db08a9093; version=a475c5dd16e57c570113eccba51955b5df8bb052 <8745d9f7e1682c39f0a1578895ac74205e2a6757; version=a475c5dd16e57c570113eccba51955b5df8bb052 <9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0; version=a475c5dd16e57c570113eccba51955b5df8bb052 <b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0; version=a475c5dd16e57c570113eccba51955b5df8bb052 <f9c9ec2c319f843b70ecdf939d48b52d189bc081

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
5.5Red HatCVSS: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-416Use After Free
CWE-825Expired Pointer Dereference
T1499Endpoint Denial of Service

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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