CVE-2026-98788 futex: Fix private hash use-after-free on resize
A use-after-free vulnerability in the Linux kernel futex subsystem allows local attackers to potentially execute code or escalate privileges.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98788?
CVE-2026-98788 is an use after free vulnerability in Linux, published on 18 Oct 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:
futex: Fix private hash use-after-free on resize
poll_state_synchronize_rcu(mm->futex.phash.batches) is used by futex_ref_drop() to check that a grace period has passed since the current hash was published. This relies on batches referencing a grace period which started after the hash pointer was assigned.
__futex_pivot_hash() sets mmph->batches before it replaces mmph->hash:
scoped_guard(rcu) { mmph->batches = get_state_synchronize_rcu(); rcu_assign_pointer(mmph->hash, new); }
The scoped_guard(rcu) doesn't stop new grace periods from starting, and if one starts between those two assignments, futex_ref_drop() can move forward while a reader still holds a pointer to the old hash.
Fix things by setting mmph->batches after assigning mmph->hash. The scoped_guard(rcu) isn't needed, so let's drop that as well.
Which versions are affected by CVE-2026-98788?
How do I fix CVE-2026-98788?
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-2026-98788 being exploited?
There is no known exploitation of CVE-2026-98788 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-98788, DEBIAN-CVE-2026-98788, GHSA-qwmc-gmgx-xf8h, UBUNTU-CVE-2026-98788.