CVE-2026-53050

What it actually does

This is a race condition in the Linux kernel quota subsystem. While quota records are being released during quota deactivation, another code path can still scan active quota entries and take a reference to an entry that is already in the release path. Under memory pressure, that stale reference can lead to use-after-free behavior, kernel warnings, memory corruption, or a kernel crash. Practical exploitation would generally require local ability to generate quota activity on a quota-enabled filesystem and to reliably hit timing-sensitive kernel behavior.

Why it matters to the business

Systems using Linux filesystems with disk quotas enabled may experience instability, crashes, or service interruption if this race is triggered. The currently reported exploitation maturity is none, EPSS is very low, and it is not listed in CISA KEV, so this should be prioritized as a kernel reliability and defense-in-depth fix rather than an emergency internet-facing exposure. However, because kernel memory-safety flaws can sometimes become local privilege-escalation primitives, organizations with multi-user Linux servers, shared hosting, build farms, container hosts, or quota-heavy storage workloads should patch during the next appropriate kernel maintenance window.

How an attack unfolds

An attacker would need access to a Linux system where filesystem quotas are enabled or quota operations are reachable through normal user activity. They would generate quota object churn, such as creating, modifying, and deleting files to force quota accounting updates, while trying to coincide with quota deactivation or release paths. If the timing is won, the quota scanning path can obtain a reference to a quota object that is already being released. Under memory pressure, that object may be freed while still being used, leading to a use-after-free condition. The most likely observable outcome is a kernel warning, oops, panic, or service disruption; successful controlled exploitation for privilege escalation is not indicated by the available intelligence.

How to fix it

Apply a Linux kernel update that includes the quota subsystem fix for the dquot_scan_active() race with quota deactivation. If vendor package names and fixed versions are not available from the advisory feed, use the fixed kernel packages published by the relevant Linux distribution or kernel supplier and confirm that the changelog references the quota/dquot_scan_active race fix. Reboot into the updated kernel after installation; merely installing the package is not sufficient if the running kernel remains vulnerable. If immediate patching is not possible, reduce exposure by disabling filesystem quotas where operationally feasible, avoiding unnecessary quota deactivation/remount activity on shared systems, limiting untrusted local shell access, and reducing local users' ability to create high-volume filesystem churn.

How to confirm the fix worked

Confirm the running kernel, not just the installed package, has been updated by checking kernel release information after reboot. Review the vendor kernel changelog or security advisory for a fix referencing dquot_scan_active(), quota deactivation, quota_release_workfn(), or use-after-free in the quota subsystem. On systems where quotas are not used, confirm quota mount options and quota services are disabled to reduce exposure. For validation testing, avoid attempting to reproduce the race on production systems because successful triggering can crash the host; use a patched staging system and verify that quota enable/disable cycles and quota-heavy filesystem activity no longer produce kernel warnings or crashes.

Typical attack path

1. Obtain local access to a Linux system that uses filesystem quotas.
2. Identify or create activity on a quota-enabled filesystem to cause repeated quota accounting changes.
3. Generate high quota churn through file creation, deletion, ownership changes, or writes that affect quota records.
4. Attempt to align quota activity with quota deactivation, unmount, remount, or quota release behavior.
5. Increase memory pressure to make stale quota-object reuse or freeing more likely.
6. Trigger the race so an active quota scan references a quota object that is being released.
7. Cause kernel warning, memory corruption, use-after-free behavior, or system crash; in a more advanced scenario, attempt to shape memory state for privilege escalation.

How to detect it

There are no public, reliable indicators of active exploitation for this issue, and successful triggering may look like a generic kernel instability event. Detection should focus on retrospective evidence of quota-related kernel warnings, crashes, use-after-free reports, or panics. Review persistent kernel logs from journald, syslog, dmesg archives, crash dump metadata, kdump/vmcore records, hypervisor reset events, and monitoring alerts for unexpected reboots. Search for stack traces or warnings involving dquot_scan_active(), quota_release_workfn(), dquot_active(), dq_list_lock, dq_count, or quota deactivation. If KASAN, KFENCE, SLUB debugging, or other kernel memory diagnostics are enabled, look for use-after-free reports involving quota or dquot structures. Correlate suspicious events with periods of high filesystem quota churn, memory pressure, unmount/remount activity, quotaoff/quotaon operations, or local users generating large numbers of file operations. Because there are no known threat actors or campaigns associated with this issue, treat findings as suspicious reliability/security events requiring triage rather than definitive compromise.

• dquot_scan_active
• quota_release_workfn
• dquot_active
• dq_list_lock
• dq_count
• releasing_dquots
• DQUOT
• quota:
• WARN_ON_ONCE
• BUG: KASAN: use-after-free
• BUG: kernel NULL pointer dereference
• kernel BUG
• Oops:
• Kernel panic
• general protection fault
• slab-use-after-free
• use-after-free in dquot
• quotaon
• quotaoff

What your security team should do

• Inventory Linux systems that use filesystem quotas, especially multi-user servers, shared hosting platforms, container hosts, storage servers, and build systems.
• Prioritize kernel updates for quota-enabled systems and systems with untrusted local users, even though the vulnerability is not currently known to be exploited and has a low EPSS score.
• Schedule and complete reboots into the fixed kernel; track systems where kernel packages were updated but the old kernel is still running.
• Temporarily disable or reduce use of filesystem quotas where feasible until patching is complete.
• Monitor kernel logs for quota-related warnings, use-after-free reports, oopses, or panics that mention dquot_scan_active(), quota_release_workfn(), or dq_count.
• If suspicious crashes occurred before patching, preserve kernel logs, crash dumps, audit logs, and workload context for forensic review.
• Ensure kernel hardening and diagnostic features such as crash dumps, persistent journald, and, where appropriate, KASAN/KFENCE in test environments are available to support detection and root-cause analysis.