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Linux KernelOperating system · Linux

CVE-2026-63804

HIGH · 7.8 CVSS v3.1 Published 2026-07-19
Fix available
A fix is available. Upgrade to 6.6.144 / 6.12.95 or later.
See remediation →
80/100
Remediation priority · High
Zero-click 4 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: gfs2: fix use-after-free in gfs2_qd_dealloc gfs2_qd_dealloc(), called as an RCU callback from gfs2_qd_dispose(), accesses the superblock object sdp through qd->qd_sbd after freeing qd. It does so to decrement sd_quota_count and wake up sd_kill_wait. However, by the time the RCU callback runs, gfs2_put_super() may have already freed sdp via free_sbd(). This can happen when gfs2_quota_cleanup() is called during unmount: it disposes of quota objects via call_rcu() and then waits on sd_kill_wait with a 60-second timeout. If the timeout expires, or if gfs2_gl_hash_clear() triggers additional qd_put() calls that schedule more RCU callbacks after the wait completes, gfs2_put_super() will proceed to free the superblock while RCU callbacks referencing it are still pending. Add an rcu_barrier() before free_sbd() in gfs2_put_super() to ensure all pending RCU callbacks (including gfs2_qd_dealloc) have completed before the superblock is freed.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-416

Memory is used after it has been freed, so its contents — now potentially attacker-controlled — drive the program's behaviour. With careful heap grooming this becomes code execution. The fix requires disciplined ownership of memory and often a targeted rework of the object lifecycle.

General guidance for the use after free class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 6.6, < 6.6.144>= 6.7, < 6.12.95>= 6.13, < 6.18.38>= 6.19, < 7.1.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 6.6.144 / 6.12.95 / 6.18.38 or later
Fixed in 6.6.1446.12.956.18.38
Recommended fix High confidence

Upgrade to kernel 6.6.144 (for 6.6.x), 6.12.95 (for 6.7-6.12.x), 6.18.38 (for 6.13-6.18.x), or 7.1.3 (for 6.19+)

  1. Update your Linux distribution's package repository to fetch the latest kernel packages
  2. Install the kernel update appropriate for your distribution (e.g., apt-get update && apt-get upgrade linux-image, or yum update kernel, or dnf upgrade kernel)
  3. Reboot the system to load the new kernel
  4. Verify the running kernel version matches or exceeds the fixed version (6.6.144, 6.12.95, 6.18.38, or 7.1.3 depending on your branch)
Caveat Kernel upgrades may require matching kernel modules or drivers; ensure compatible userspace tools and GFS2 utilities are available after upgrade

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $3,200. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-63804 in production — separate from our analysis above.

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What this is

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