CVE-2026-23248: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-23248 is a use-after-free (UAF) vulnerability in the Linux kernel's perf/core subsystem, specifically within the perf_mmap() function. It was discovered and disclosed on March 18, 2026, affecting Linux kernel versions 6.14 through 6.18.16 and 6.19 through 6.19.6, as well as the 7.0-rc1 release. The vulnerability stems from a race condition that can lead to refcount corruption and potential UAF when concurrent mmap() operations are performed on dependent perf events. It carries a CVSS v3.1 base score of 7.8 (High) (Red Hat Advisory, Red Hat Bugzilla).

The root cause is classified as CWE-416 (Use After Free), triggered by a race condition in perf_mmap(). During mmap setup, the ring buffer (rb) is allocated and assigned to event->rb while mmap_mutex is held; the mutex is then released to call map_range(). If map_range() fails, perf_mmap_close() is invoked for cleanup — but because the mutex was dropped, a concurrent thread (e.g., via inherited events or output redirection) can acquire the mutex, observe the valid event->rb pointer, and attempt to increment its reference count. If the cleanup path has already decremented the refcount to zero, the concurrent increment results in a use-after-free or refcount saturation warning, as originally reported by Syzkaller. The fix extends mmap_mutex scope to cover the map_range() call, ensuring atomic initialization and cleanup (Red Hat Bugzilla, Kernel Patch 1).

A local user with privileges to use perf events can trigger the race condition between concurrent mmap() operations on dependent events, causing a use-after-free condition that may allow arbitrary local code execution or kernel crash (denial of service). The vulnerability affects confidentiality, integrity, and availability — all rated High — since successful exploitation could grant an attacker elevated privileges or destabilize the kernel. The attack is limited to local access and requires low privileges (e.g., access to perf event syscalls), but does not require user interaction (Red Hat Advisory).

Update the Linux kernel to a patched version: 6.18.17, 6.19.7, or 7.0-rc2 or later. Patches are available in the upstream stable kernel branches (Kernel Patch 1, Kernel Patch 2, Kernel Patch 3). As a workaround, restrict unprivileged access to perf events by setting kernel.perf_event_paranoid to a restrictive value (e.g., 3) via sysctl, or limit perf event capabilities to trusted users only. Amazon Linux 2023 users should apply the update referenced in ALAS2023-2026-1596.

Red Hat tracked the issue via Bugzilla (Bug 2448596) and assigned it a medium severity rating, with the upstream advisory published on the Linux kernel CVE announce mailing list by Greg Kroah-Hartman (Red Hat Bugzilla). Microsoft also acknowledged the vulnerability in its Security Response Center update guide, noting its relevance to the Azure Linux 3 kernel (Microsoft MSRC). No significant broader community or social media discussion has been observed beyond standard vulnerability tracking.