CVE-2026-23248 perf/core: Fix refcount bug and potential UAF in perf_mmap
A race condition in the Linux kernel perf subsystem allows a use-after-free, potentially enabling local attackers to execute code or escalate privileges.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23248?
CVE-2026-23248 is a high-severity use after free vulnerability in Linux kernel, published on 18 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-23248?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-23248?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-23248 being exploited?
There is no known exploitation of CVE-2026-23248 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-23248, DEBIAN-CVE-2026-23248, GHSA-78fw-h7fp-fffh, ROOT-OS-UBUNTU-2204-CVE-2026-23248, ROOT-OS-UBUNTU-2404-CVE-2026-23248, UBUNTU-CVE-2026-23248.