CVE-2026-52923: Linux Kernel IPC Checkpoint/Restore Use-After-Free Vulnerability

Technical summary

CVE-2026-52923 is a resource exhaustion and use-after-free vulnerability in the Linux kernel's IPC subsystem, specifically in the ipc_idr_alloc() function. The checkpoint/restore path requests System V IPC allocations via ids->next_id, forwarding requests to idr_alloc() with an unbounded upper limit (zero). Once the valid SysV IPC tail (bounded by ipc_mni) fills, idr_alloc() allocates beyond the valid range. The kernel encodes the allocated index into the object ID using the narrower SysV IPC encoding, creating an index mismatch. Subsequent removal via ipc_rmid() truncates the real IDR index during lookup, leaving dangling pointers in the IDR data structure. Proc filesystem walks (/proc/sysvipc/shm) then dereference freed memory. The fix bounds allocation requests to ipc_mni, causing checkpoint/restore to fail gracefully once the valid range exhausts.

Business impact

This vulnerability affects any deployment relying on container checkpoint/restore functionality or SysV IPC-heavy workloads running on vulnerable kernels. In cloud and containerization environments, triggering this bug could cause service disruption through kernel panics or memory corruption. The ability to dereference freed memory increases the window for privilege escalation or information disclosure if an attacker can control the timing and content of freed memory regions. Organizations using Kubernetes or similar platforms with container migration features should assess their exposure, as this vulnerability is reachable by unprivileged local processes.

Affected systems

All versions of the Linux kernel implementing the IPC subsystem are affected. The vulnerability exists in the checkpoint/restore code path, making any kernel with CONFIG_CHECKPOINT_RESTORE enabled vulnerable. Container orchestration systems (Kubernetes, Docker, OpenStack) that depend on kernel checkpoint/restore capabilities for live migration or process snapshotting are in scope. The bug is architectural to how SysV IPC ID allocation works and has no version cutoff; verify against upstream Linux kernel advisories and your distribution's kernel changelog for specific affected stable release versions.

Exploitability

Exploitation requires local system access with unprivileged user privileges (PR:L in the CVSS vector). No network access is needed. The attack is deterministic: an attacker fills the SysV IPC namespace to its limit, then triggers a checkpoint/restore allocation request, causing the kernel to allocate out-of-range. Subsequent proc enumeration dereferences the stale pointer. The attack surface is accessible to any local user and does not require special capabilities. Exploitation is feasible for motivated attackers but not trivial, as it requires understanding and triggering the checkpoint/restore path under specific namespace saturation conditions.

Remediation

Apply a kernel patch that bounds ipc_idr_alloc() requests to ipc_mni, preventing allocation beyond the valid SysV IPC range. This causes checkpoint/restore to fail cleanly once capacity is exhausted, rather than corrupting the IDR state. Patch availability depends on your Linux distribution and kernel branch. Check your vendor's security advisory for backported fixes to stable kernels. Temporary mitigation: disable CONFIG_CHECKPOINT_RESTORE at compile time if live migration is not required, or restrict access to the checkpoint/restore sysctl interface via LSM policies.

Patch guidance

Identify your running kernel version using `uname -r`. Cross-reference with your distribution's security bulletin for CVE-2026-52923. Major distributions (Red Hat, Canonical, SUSE, Debian) will publish backported kernel packages; prioritize applying these as standard security updates. For mainline kernels, look for commits addressing ipc_idr_alloc() boundary enforcement in the kernel stable trees. Verify the patch modifies the upper bound parameter in the idr_alloc() call from 0 to ipc_mni. After patching, reboot to activate the new kernel.

Detection guidance

Monitor for kernel warnings or panics mentioning 'IDR' or 'ipc' in the kernel log (journalctl, dmesg). Detection of active exploitation is difficult without intrusion detection tuned to SysV IPC namespace behavior. Organizations can audit sysctl writes to ipcs_idr or checkpoint/restore interface usage via auditd rules targeting 'msgget', 'shmget', and 'semget' syscalls under sustained namespace pressure. Proc filesystem reads of /proc/sysvipc/shm that precede kernel crashes may indicate exploitation attempts. Set up alerts for kernel panics in containers or VMs performing live migration.

Why prioritize this

This vulnerability merits immediate but not emergency attention. The CVSS score of 7.8 (HIGH) reflects local-only reach and the need for unprivileged access, yet the impact potential includes both confidentiality (memory leaks) and availability (DoS via panic). Organizations with active checkpoint/restore usage—primarily cloud and container platforms—should prioritize patching within standard monthly security cycles. Non-containerized or isolated deployments with disabled checkpoint/restore can defer, pending their next major kernel update.

Risk score, explained

The CVSS 3.1 score of 7.8 is derived from: Attack Vector=Local (reduces scope), Attack Complexity=Low (straightforward exploitation once conditions are met), Privileges Required=Low (unprivileged user), User Interaction=None (automatic upon trigger), Confidentiality/Integrity/Availability all High (use-after-free can corrupt memory, leak data, and crash the kernel). The score reflects the seriousness of memory safety issues balanced against the local-only attack surface.

Frequently asked questions