---
id: "CVE-2026-98788"
kind: "vulnerability"
aliases: ["CVE-2026-98788"]
title: "Linux kernel: futex private hash resize can free memory still in use"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["futex", "linux-kernel", "runtime"]
not_affected_if: []
published_at: "2026-10-18T16:17:32+00:00"
first_seen_at: "2026-10-23T21:57:16+00:00"
updated_at: "2026-10-25T05:15:15+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98788", "first_seen_at": "2026-10-23T21:57:16+00:00"}]
---

# Linux kernel: futex private hash resize can free memory still in use

When the kernel resizes a process's private futex hash table, a race can let the old table be freed while a reader still holds a pointer to it. The sources do not say what an attacker can do with the freed memory beyond the use-after-free itself.

_Summary, check and fix written by a model from the sources; labelled as such._

## Timeline

- 2026-10-23T21:57:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98788

## From the sources

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.

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