The Linux kernel tracing vulnerability (CVE-2026-64028) involves the hist_field_name() function returning NULL unexpectedly when truncation occurs during string formatting in a fully-qualified VAR_REF/EXPR case. This NULL return bypasses the usual NULL-to-empty-string guard, causing subsequent strcat() and strcmp() calls to dereference NULL pointers. The root cause is that the field name, derived from a histogram variable name parsed from a trigger string, lacks a length cap, allowing sufficiently long names to trigger truncation and the NULL return. The patch modifies the function to retain the length check but ensures that on overflow the field_name is set to an empty string instead of NULL, preventing NULL pointer dereferences.

The vulnerability can lead to NULL pointer dereferences in kernel code paths related to tracing histograms, potentially causing kernel crashes or denial of service. There is no indication of code execution or privilege escalation. No known exploits in the wild have been reported.

A fix has been implemented in the Linux kernel to address this issue by modifying hist_field_name() to avoid returning NULL on truncation. Since this is a kernel vulnerability, applying the official kernel update or patch that includes this fix is the recommended remediation. Patch status is not explicitly confirmed in the provided data; users should consult the official Linux kernel advisories or repositories for the updated fixed version.