CVE-2026-89771: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-89771 is a race condition vulnerability in the Linux kernel's ring buffer subsystem that can lead to denial of service. The flaw exists in the ring_buffer_read_page() and ring_buffer_read_start() functions, which read trace_buffer::subbuf_size without proper locking while ring_buffer_subbuf_order_set() can concurrently resize the buffer. Affected kernel versions begin at 6.8 (introduced at commit f9b94daa542a); fixed versions include 6.12.109, 6.18.50, 7.2.4, and 7.3-rc1. The vulnerability is rated Medium severity with an EPSS score of 0.0 (Red Hat Advisory, Red Hat Bugzilla).

The root cause is a race condition within a thread (CWE-366), specifically a time-of-check/time-of-use (TOCTOU) issue (CAPEC-29) in the Linux kernel's tracing ring buffer. The trace_buffer::subbuf_size field is read locklessly in ring_buffer_read_page() and ring_buffer_read_start(), while ring_buffer_subbuf_order_set() can simultaneously modify the buffer's subpage order, resulting in inconsistent size references between the reader and the buffer state. The fix replaces lockless reads of trace_buffer::subbuf_size with reads of bpage::order, holds the trace_buffer mutex in ring_buffer_read_start() to synchronize with pending buffer order modifications, removes the now-redundant subbuf_size field, and introduces new accessor functions rb_subbuf_capacity(), rb_page_capacity(), and rb_subbuf_size() (Red Hat Advisory, Red Hat Bugzilla).

A local user with read access to the kernel ring buffer can trigger the race condition by concurrently reading from and resizing the buffer, causing buffer read operations to use stale or inconsistent size values. This can lead to buffer overflows, kernel data corruption, or kernel crashes, resulting in a denial of service condition. The impact is limited to availability; there is no evidence of confidentiality or integrity compromise beyond potential data corruption within the tracing subsystem (Red Hat Bugzilla, Red Hat Advisory).

There is no public proof-of-concept exploit and no evidence of in-the-wild exploitation as of the disclosure date. The vulnerability requires local access to the system and the ability to interact with the kernel ring buffer (e.g., via the tracing subsystem). The EPSS score is 0.0, and the CVE is not listed in the CISA Known Exploited Vulnerabilities catalog. No threat actor attribution has been reported (Red Hat Advisory, GitHub Advisory).

Apply the upstream kernel patches that address the race condition. Fixed versions are available at Linux kernel 6.12.109, 6.18.50, 7.2.4, and 7.3-rc1. The specific fix commits are 6d666f0b8b36, 50f4a793c4ff, 0c7c517827a4, and 8a5f63637890 in the stable kernel tree. Users should update to a patched kernel version provided by their Linux distribution as soon as it becomes available. As a temporary measure, restricting unprivileged access to the kernel tracing subsystem (e.g., via kernel.perf_event_paranoid or limiting access to /sys/kernel/tracing/) may reduce exposure (Red Hat Advisory, Red Hat Bugzilla).

The vulnerability received routine coverage in CVE aggregation feeds and was briefly mentioned in a Reddit daily CVE brief on September 12, 2026. No notable researcher commentary or significant media coverage has been identified beyond standard vulnerability database entries (Red Hat Bugzilla).