CVE-2026-99063 Linux CVE debrief

Who should care

Linux system administrators, security teams, and users with access to the `dm ioctl` interface should assess their exposure and apply patches or mitigations as necessary. Linux system administrators and security teams should verify and apply patches for affected kernel versions. The vulnerability is not a security bug but can be triggered by a `DM_LIST_DEVICES` request with a `data_size` of 305 bytes.

Why it matters

The Linux kernel vulnerability CVE-2026-99063 allows an out-of-bounds read in the `dm ioctl` system. While not a security bug, it can be triggered by a `DM_LIST_DEVICES` request with a `data_size` of 305 bytes. Linux system administrators and security teams should verify and apply patches for affected kernel versions.

• Verify Linux kernel versions and apply patches to fix the vulnerability
• Restrict access to the `dm ioctl` interface for unprivileged users
• Monitor system logs for potential exploitation attempts

Technical summary

The Linux kernel vulnerability CVE-2026-99063 allows an out-of-bounds read in the `dm ioctl` system when `data_start` exceeds the buffer size. The issue arises from the `get_result_buffer` function setting `data_start` to `sizeof(struct dm_ioctl)` without considering the actual buffer size. This can be triggered by a `DM_LIST_DEVICES` request with a `data_size` of 305 bytes, causing the system to read beyond the allocated buffer. The vulnerability has been fixed by clamping `data_start` to the buffer size, preventing the out-of-bounds read.

Defensive priority

Verify and apply patches for Linux kernel versions affected by this vulnerability, particularly for systems where unprivileged users have access to the `dm ioctl` interface.

Recommended defensive actions

• Verify Linux kernel versions and apply patches to fix the vulnerability
• Restrict access to the `dm ioctl` interface for unprivileged users
• Monitor system logs for potential exploitation attempts
• Perform a thorough review of system configurations and user access to the `dm ioctl` interface
• Implement additional monitoring and logging to detect potential exploitation attempts
• Conduct a risk assessment to determine the potential impact of the vulnerability on the organization
• Develop a plan to apply patches or mitigations to affected systems

Evidence notes

The CVE record and source item provide details on the vulnerability, including its resolution in the Linux kernel. The NVD entry is currently not provided. The vulnerability allows an out-of-bounds read in the `dm ioctl` system when `data_start` exceeds the buffer size. The issue arises from the `get_result_buffer` function setting `data_start` to `sizeof(struct dm_ioctl)` without considering the actual buffer size. This can be triggered by a `DM_LIST_DEVICES` request with a `data_size` of 305 bytes, causing the system to read beyond

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.