CVE-2026-53050: Linux Kernel Quota Race Condition Use-After-Free

Technical summary

CVE-2026-53050 involves a synchronization flaw in the Linux kernel's disk quota subsystem, specifically between dquot_scan_active() and quota_release_workfn(). The race occurs because quota objects marked for release (DQ_ACTIVE_B flag still set, dq_count == 0) can be scanned and incremented before being properly removed from the active quota list. After the SRCU (Sleepable Read-Copy-Update) synchronization point in quota_release_workfn(), the releasing dquot may be freed while dquot_scan_active() holds an incremented reference, creating a use-after-free scenario. The fix ensures that dquots are atomically removed from the releasing list when a reference is acquired during scanning.

Business impact

For systems managing disk quotas (common in multi-tenant environments, HPC clusters, and shared hosting platforms), this vulnerability can result in kernel panics, denial of service through quota enforcement failures, or potential data integrity issues when quota limits are unexpectedly enforced or unenforced. Organizations relying on quota-based resource isolation may experience service interruptions or unpredictable quota behavior during periods of active quota reclamation.

Affected systems

The Linux kernel is affected across multiple versions (exact patched versions should be verified against kernel.org advisories). Any system running a vulnerable kernel with disk quotas enabled (CONFIG_QUOTA) is at risk. This includes enterprise Linux distributions (Red Hat Enterprise Linux, Ubuntu, Debian, SUSE), cloud platforms using Linux kernels, and any infrastructure where disk quota enforcement is active.

Exploitability

Exploitation requires local access and valid user credentials on the target system. An attacker cannot trigger this remotely; they must be able to execute code as a local user and actively perform quota-related operations that trigger the race condition. The vulnerability is non-trivial to exploit reliably due to the tight timing requirement, but the consequences (use-after-free) are severe if achieved. The race becomes more likely to manifest under sustained memory pressure or high quota activity.

Remediation

Patch the Linux kernel to a version containing the fix for CVE-2026-53050. The resolution involves ensuring atomic removal of dquots from the releasing list before references are acquired by scanning threads. Verify the specific patched kernel version from your distribution's security advisory, as version numbers vary across Linux distributions. Until patching is possible, limiting local access and monitoring quota-related system calls can reduce exposure.

Patch guidance

Obtain and deploy the latest kernel security update from your Linux distribution (verify against vendor advisories for RHEL, Ubuntu, Debian, SUSE, etc.). Ensure CONFIG_QUOTA is enabled in your kernel build if quotas are in use; if quotas are not required, they can be disabled at build time. Test kernel updates in a staging environment before production deployment, particularly for systems with active quota usage. Allow for scheduled downtime for kernel reboots.

Detection guidance

Monitor for kernel warnings logged by the original WARN_ON_ONCE() condition ("atomic_read(&dquot->dq_count)" unexpectedly non-zero during dquot deactivation). Enable audit logging for quota-related syscalls (quotactl) to identify periods of high quota activity that might trigger the race. Inspect system logs for use-after-free warnings or kernel panics that correlate with quota operations. On unpatched systems, elevated kernel crash rates coupled with active quota management can indicate exploitation or natural race condition triggers.

Why prioritize this

Although exploitation requires local access and valid credentials, the CVSS 3.1 score of 7.8 (HIGH) reflects the severity of the consequences: potential kernel crash, denial of service, and data integrity compromise. Prioritize patching for systems where quota enforcement is security-critical or where multiple local users have access. Systems with tight disk quota policies in multi-tenant scenarios should be considered higher priority.

Risk score, explained

The CVSS 3.1 score of 7.8 is derived from local attack vector (AV:L), low attack complexity (AC:L), requiring low privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), and high impact across confidentiality, integrity, and availability (C:H/I:H/A:H). The score reflects that while local access is mandatory, the resulting use-after-free can fully compromise system reliability and data integrity under memory pressure, justifying the HIGH severity rating.

Frequently asked questions