CVE-2026-64249: Linux Kernel Use-After-Free Vulnerability

CVE-2026-64249 Overview

CVE-2026-64249 is a use-after-free vulnerability in the Linux kernel's Field Programmable Gate Array (FPGA) region subsystem. The flaw resides in the child_regions_with_firmware() function, where of_node_put(child_region) releases a device tree node reference before pr_err() dereferences the same pointer. This ordering causes the kernel to access freed memory during error logging paths. The upstream fix reorders the calls so that the error message prints before the reference is released. Multiple stable kernel branches received corresponding backports.

Critical Impact
A use-after-free in kernel FPGA region handling can lead to memory corruption or information disclosure when the error path is triggered.

Affected Products

Linux kernel (FPGA region subsystem)
Multiple stable kernel branches with backported fixes
Systems using device tree-based FPGA region configuration

Discovery Timeline

2026-07-24 - CVE-2026-64249 published to NVD
2026-07-30 - Last updated in NVD database

Technical Details for CVE-2026-64249

Vulnerability Analysis

The vulnerability exists in the FPGA region driver code that manages child regions declared in the device tree. When the driver iterates through child regions to validate firmware requirements, the error-handling path calls of_node_put() on the child_region device tree node before the subsequent pr_err() call references that same node for diagnostic output. Once of_node_put() drops the final reference, the underlying device_node structure can be freed. Any dereference by pr_err() afterward reads memory that no longer belongs to the caller.

The class of defect is [CWE-416] Use After Free. In kernel context, use-after-free conditions can escalate into read primitives, write primitives, or kernel panics depending on allocator behavior and adjacent object reuse. The fix moves the of_node_put(child_region) call to occur after the pr_err() reference, ensuring the node remains valid during logging.

Root Cause

The root cause is incorrect ordering of reference count release and pointer use in an error path. The device tree node reference was decremented before its final consumer completed, violating the acquire-use-release contract expected by the of_node_put() helper.

Attack Vector

Exploitation requires reaching the error branch inside child_regions_with_firmware(). This typically depends on local access to configure FPGA regions or supply malformed device tree overlays. The NVD entry does not currently assign a CVSS score or attack vector. Practical impact depends on which allocator slab reclaims the freed node and whether attacker-controlled data can be placed into that slab before pr_err() dereferences it.

No verified public exploit code is available. Refer to the upstream commit reference for the exact patch diff.

Detection Methods for CVE-2026-64249

Indicators of Compromise

Kernel oops or panic messages referencing child_regions_with_firmware in the call trace
KASAN (Kernel Address Sanitizer) use-after-free reports naming of_node_put or fpga_region
Unexpected FPGA region initialization failures accompanied by memory corruption warnings

Detection Strategies

Enable KASAN on test kernels to surface use-after-free access during FPGA region probe
Compare running kernel version and backport status against the eight stable commit references listed by kernel.org
Audit device tree overlays applied at runtime that instantiate FPGA regions with firmware attributes

Monitoring Recommendations

Forward kernel ring buffer (dmesg) output to centralized logging and alert on fpga_region error patterns
Track kernel package versions across Linux fleets to confirm patched builds are deployed
Monitor for repeated FPGA region probe failures that may indicate exploitation attempts

How to Mitigate CVE-2026-64249

Immediate Actions Required

Apply the stable kernel updates that include the commits referenced by kernel.org for this CVE
Rebuild and redistribute custom kernels that carry the FPGA region driver with the fix applied
Restrict access to interfaces that load device tree overlays or configure FPGA regions to trusted administrators

Patch Information

The upstream fix reorders of_node_put(child_region) to occur after the pr_err() call. Backports are available across multiple stable branches. See the following patch references:

Workarounds

Disable the FPGA region driver (CONFIG_FPGA_REGION) in kernel configuration where FPGA functionality is not required
Prevent loading of untrusted device tree overlays that declare FPGA child regions
Limit local access to systems exposing FPGA management interfaces until patched kernels are deployed