CVE-2026-97959 net/sched: cls_route: free emptied bucket on filter move
A memory leak in the Linux kernel's route classifier allows local attackers to exhaust kernel memory, causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-97959?
CVE-2026-97959 is a memory corruption vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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 '
Which versions are affected by CVE-2026-97959?
How do I fix CVE-2026-97959?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-97959 being exploited?
There is no known exploitation of CVE-2026-97959 in the wild and no public exploit code.
Sources
Also known as AZL-104640, BELL-CVE-2026-97959, DEBIAN-CVE-2026-97959, GHSA-q5gc-9c5f-rc6r, UBUNTU-CVE-2026-97959.