CVE-2026-53312: Linux Kernel RISC-V IOMMU Infinite Loop Denial of Service

Technical summary

CVE-2026-53312 addresses an infinite loop vulnerability in the RISC-V IOMMU invalidation path within the Linux kernel. The vulnerability occurs because the code does not properly handle overflow conditions when gather->end equals ULONG_MAX, a value that should be valid for sign-extended page tables on RISC-V architecture. Additionally, the length computation during invalidation can overflow, compounding the problem. The fix involves moving arithmetic operations to prevent overflow—specifically relocating the +1 operation in the length calculation to avoid integer overflow conditions that trigger the infinite loop.

Business impact

This vulnerability enables a local, unprivileged user to cause a kernel hang or system unresponsiveness by triggering the IOMMU invalidation path with specially crafted parameters. On systems relying on RISC-V processors and using the IOMMU for device isolation or memory protection, a successful exploit results in denial of service. The impact is localized to availability; confidentiality and integrity are not affected. Systems handling sensitive workloads or requiring high availability may face service disruptions if exploitation occurs.

Affected systems

The vulnerability affects the Linux kernel across RISC-V-based systems that utilize the IOMMU functionality. This includes RISC-V server platforms, embedded systems with IOMMU-capable processors, and virtualized RISC-V environments. The vulnerable code path is only reachable on systems where RISC-V IOMMU support is compiled into or as a module in the kernel. Systems without RISC-V IOMMU enabled are unaffected. Specific kernel versions prior to the patch are vulnerable; consult the official Linux kernel security advisories for exact affected version ranges.

Exploitability

The vulnerability requires local access to the system and low privilege level (user-space caller) to trigger. No special capabilities or authentication beyond basic user access are needed. The exploit path involves invoking IOMMU invalidation operations through available kernel interfaces with parameters designed to hit the overflow condition. The attack is reliable and does not require user interaction or specific system configurations beyond RISC-V IOMMU support being enabled. Network-based or remote exploitation is not possible.

Remediation

The primary remediation is to apply the upstream Linux kernel patch that fixes the overflow handling in the RISC-V IOMMU invalidation code. The patch modifies the arithmetic logic to prevent both the infinite loop condition when gather->end equals ULONG_MAX and the overflow in length computation. Until patching is feasible, system administrators can mitigate by restricting local user access on affected systems or disabling RISC-V IOMMU support if not critical to operations, though the latter may degrade security posture or functionality.

Patch guidance

Obtain and apply the official Linux kernel patch for CVE-2026-53312 from the Linux kernel security advisories or your distribution's security update channel. Verify the patch addresses both the infinite loop condition and the length computation overflow. For distributions providing kernel updates, check security bulletins from Red Hat, Ubuntu, Debian, or other vendors supporting RISC-V platforms for availability and timing. Test patched kernels in non-production environments before wide deployment to ensure compatibility with your RISC-V hardware and device configurations. After patching, a reboot is required to apply kernel changes.

Detection guidance

Monitor for signs of kernel unresponsiveness or hangs specifically on RISC-V systems with IOMMU enabled. Elevated CPU usage from kernel threads handling IOMMU operations may indicate an active infinite loop. Kernel logs or dmesg output may show IOMMU invalidation requests that do not complete. For proactive detection, implement kernel auditing to capture IOMMU invalidation operation invocations and flag those with end addresses at or near ULONG_MAX. Security tools that profile system call activity can help identify user-space processes repeatedly triggering IOMMU operations.

Why prioritize this

This vulnerability merits prompt attention because it enables local denial of service on RISC-V systems with IOMMU support. While not exploitable remotely and requiring local access, the low complexity of the attack, combined with the potential to render systems unresponsive, justifies prioritization on affected RISC-V deployments. The CVSS score of 5.5 (Medium) reflects the availability impact, but organizations running RISC-V platforms should not delay patching given the straightforward attack surface.

Risk score, explained

The CVSS:3.1 vector (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) assigns a score of 5.5 (Medium). Attack Vector Local and low Attack Complexity indicate the vulnerability is easily reachable and reliable to exploit. Privileges Low and no User Interaction required mean unprivileged users can trigger it without additional steps. The scope remains unchanged, and while Confidentiality and Integrity are not impacted, Availability is rated High due to the denial of service nature of the infinite loop. The Medium rating appropriately reflects that this is a serious availability issue on affected systems but lacks the amplification factors of network-exploitable vulnerabilities.

Frequently asked questions