CVE-2026-52930: Linux Kernel Shared Memory Synchronization Race Condition

Technical summary

The vulnerability is a synchronization race condition in ipc/shm.c, specifically in the shm_destroy_orphaned() function. The function traverses the shared memory IDR under shm_ids(ns).rwsem, but the shm_may_destroy() check it performs is not atomic with respect to shm_nattch field updates, which occur under shm_perm.lock during attach operations. The attach path can modify shm_nattch without holding the rwsem, creating a window where shm_may_destroy() may return true based on stale data. The fix moves the shm_may_destroy() check into the critical section protected by shm_perm.lock, ensuring the decision to destroy and the actual state of the segment are consistent. This matches the synchronization discipline already used by other destroy paths in the codebase.

Business impact

This vulnerability enables local denial of service attacks against systems relying on shared memory semantics. An attacker with local user privileges can exploit the race condition to cause kernel instability, potentially leading to system crashes, application hangs, or loss of service availability. Multi-tenant environments and containerized deployments are particularly exposed, as tenant isolation depends on correct memory management. Production systems running affected kernels may experience unexpected downtime if actively exploited.

Affected systems

All Linux kernel versions prior to the patch are affected. The vulnerability requires local access and is triggered during shared memory lifecycle operations (attach/detach/cleanup cycles). Systems with active IPC shared memory usage—particularly those using System V IPC or legacy applications—are most at risk. Embedded Linux systems, IoT devices, and containerized environments running on affected kernels are vulnerable.

Exploitability

Exploitation requires local user-level access and a reasonable understanding of IPC shared memory behavior. The attacker must trigger race conditions by carefully timing attach and orphan cleanup operations. While not trivial to exploit reliably, the attack surface is straightforward: any local user can attempt to trigger shared memory attach/detach cycles to manipulate segment lifecycle. The local-only requirement (AV:L) limits external attack vectors but does not mitigate insider or multi-tenant scenarios.

Remediation

Apply a kernel update that includes the patch moving shm_may_destroy() into the shm_perm.lock critical section. Verify against your vendor's security advisory for the specific patched kernel version for your distribution. Until patching is complete, restrict local user access and disable System V IPC shared memory if it is not required for legacy applications.

Patch guidance

Check your Linux distribution's security advisory for CVE-2026-52930 to identify the patched kernel version. Typical patch workflows: (1) identify your current kernel version via 'uname -r'; (2) obtain the patched kernel from your vendor (e.g., RHEL, Ubuntu, Debian security repositories); (3) test the update in a non-production environment to verify application compatibility; (4) schedule and deploy the kernel update with appropriate maintenance windows; (5) verify the patch is in place post-reboot using 'uname -r' and checking kernel logs for any IPC-related warnings. Kernel updates typically require a reboot to take effect.

Detection guidance

Monitor kernel logs for messages related to shared memory cleanup, particularly any warnings or oops messages involving ipc/shm functions. System administrators can use 'ipcs -m' to enumerate active shared memory segments and 'ipcrm' to inspect segment details. In forensic analysis, look for evidence of rapid attach/detach cycles in process syscall traces. Kernel address sanitizers (KASAN) and lock debugging (CONFIG_DEBUG_SPINLOCK, CONFIG_DEBUG_RWSEMS) may expose the race condition under load; enable these in test environments to validate patches before production deployment.

Why prioritize this

Although the CVSS score is moderate (5.5), prioritize this as a high-concern item for systems with multi-tenant workloads or where application availability is critical. The denial of service impact is direct and can affect dependent services. The local-only attack vector reduces urgency for internet-facing systems, but privilege isolation within a single host depends on correct kernel behavior. Prioritize patch deployment for systems running IPC-intensive workloads (databases, message queues, legacy middleware).

Risk score, explained

The CVSS 3.1 score of 5.5 (Medium) reflects local access requirement (AV:L), low attack complexity (AC:L), low privilege escalation needed (PR:L), user interaction not required (UI:N), and impact scoped to the affected system (S:U). Availability impact is high (A:H) due to potential kernel crash. Confidentiality and integrity are not affected. The moderate score appropriately weights the denial of service severity against the local-only attack vector. Organizations with strict SLA requirements or multi-tenant architectures should treat this as higher priority than the score alone suggests.

Frequently asked questions