In the Linux kernel, the following vulnerability has been resolved: perf/core: Fix refcount bug and potential UAF in perf_mmap Syzkaller reported a refcount_t: addition on 0; use-after-free warning in perf_mmap. The issue is caused by a race condition between a failing mmap() setup and a concurrent mmap() on a dependent event (e.g., using output redirection). In perf_mmap(), the ring_buffer (rb) is allocated and assigned to event->rb with the mmap_mutex held. The mutex is then released to perform map_range(). If map_range() fails, perf_mmap_close() is called to clean up. However, since the mutex was dropped, another thread attaching to this event (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 dropped the reference count to zero, this results in a use-after-free or refcount saturation warning. Fix this by extending the scope of mmap_mutex to cover the map_range() call. This ensures that the ring buffer initialization and mapping (or cleanup on failure) happens atomically effectively, preventing other threads from accessing a half-initialized or dying ring buffer.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - perf/core: Fix refcount bug and potential UAF in perf_mmap Syzkaller reported a refcount_t: addition on 0;
    use-after-free warning in perf_mmap. The issue is caused by a race condition between a failing mmap()     setup and a concurrent mmap() on a dependent event (e.g., using output redirection). In perf_mmap(), the     ring_buffer (rb) is allocated and assigned to event->rb with the mmap_mutex held. The mutex is then     released to perform map_range(). If map_range() fails, perf_mmap_close() is called to clean up. However,     since the mutex was dropped, another thread attaching to this event (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 dropped the reference count to zero, this results in a     use-after-free or refcount saturation warning. Fix this by extending the scope of mmap_mutex to cover the     map_range() call. This ensures that the ring buffer initialization and mapping (or cleanup on failure)     happens atomically effectively, preventing other threads from accessing a half-initialized or dying ring     buffer. (CVE-2026-23248)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
329305	openSUSE 16: cluster-md-kmp-64kb / cluster-md-kmp-azure / cluster-md-kmp-default / etc (openSUSE-SU-2026:21388-1)	Nessus	SuSE Local Security Checks	high
311340	Amazon Linux 2023 : bpftool6.18, kernel6.18, kernel6.18-devel (ALAS2023-2026-1596)	Nessus	Amazon Linux Local Security Checks	high
302906	Linux Distros Unpatched Vulnerability : CVE-2026-23248	Nessus	Misc.	high

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CVE-2026-23248

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