CVE-2026-64366 Linux CVE debrief

Who should care

Defenders responsible for Linux kernel security, particularly those managing Linux-based systems with HID: wacom modules, should assess exposure and prioritize patching to prevent potential slab-out-of-bounds write exploitation. This includes operators, platform administrators, vulnerability management teams, and security teams who need to verify Linux kernel versions, apply patches, and monitor system logs for potential exploitation attempts.

Why it matters

The vulnerability allows for a slab-out-of-bounds write in the Linux kernel's HID: wacom module, potentially leading to system compromise.

• Verify Linux kernel versions to identify potentially vulnerable systems.
• Apply patches to prevent slab-out-of-bounds write exploitation.
• Monitor system logs for potential exploitation attempts.

Technical summary

The vulnerability exists in the Linux kernel's HID: wacom module, specifically in the wacom_wac_queue_insert function. The function calls kfifo_skip in a loop when the kfifo does not have enough space for the incoming report. If the kfifo is empty, kfifo_skip reads stale data left in the kmalloc'd buffer and interprets it as a record length, advancing fifo->out by that garbage value. This corrupts the internal kfifo state, causing kfifo_unused to return a value much larger than the actual buffer size, which bypasses __kfifo_in_r's guard. kfifo_copy_in then performs an out-of-bounds memcpy, writing up to 3842 bytes past the 256-byte buffer.

Defensive priority

Defenders should prioritize verifying the Linux kernel version and applying patches to fix the vulnerability.

Recommended defensive actions

• Verify the Linux kernel version and compare it to the known affected versions.
• Apply patches to fix the vulnerability.
• Monitor system logs for potential exploitation attempts.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The vulnerability was resolved in the Linux kernel. The fix involves adding a !kfifo_is_empty condition to the while loop so kfifo_skip is never called on an empty fifo, and checking the return value of kfifo_in to reject reports that are too large for the fifo.

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.