Live › vulnerability › CVE-2026-98811
Go to dashboardTwo racing tc filter add requests on the same chain and priority can leave an empty classifier proto linked in the kernel after both fail, holding references to the chain, block and classifier module. The sources describe a resource leak rather than code execution or privilege escalation.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 21:57 UTC. All times on this page are UTC.
Systems where unprivileged or namespaced users can run tc filter commands with CAP_NET_ADMIN, which the sources say unshare -Urn is enough to do. Hosts that never run tc or use flower classifiers with untrusted local users are unlikely to matter. unknown for the exact kernel version range.
No product ranges from the sources yet.
uname -r and compare with the fixed kernel in the NVD record or your distribution's advisorytc filter show dev <iface> ingress and look for a bare filter protocol ip pref 1 flower chain 0 header with no filter entriesCONFIG_NET_CLS_FLOWER is enabled in your kernel configEach row is the first time that source carried this signal. The analyst’s rows are its own findings.
In the Linux kernel, the following vulnerability has been resolved:
net/sched: cls_api: reclaim an empty proto on the error path
Two racing tc filter add requests on the same chain/prio of an unlocked classifier both run change() on the shared proto and both can fail: the winner's tcf_chain_tp_delete_empty() attempt gives up because the loser's handle is still in the idr, and the loser's error path drops only its own reference without a second reclamation attempt. The empty proto stays linked in the chain, holding the chain reference, a block reference and the classifier module reference until the chain or block is torn down.
Reclaim the proto on the error path of any failed request that holds a proto reference. The reclamation is emptiness-gated: tcf_chain_tp_delete_empty() unlinks the proto only when delete_empty() admits it is empty, so a live shared proto is never unlinked. A proto the request created is reclaimed unconditionally - it is the only owner, so marking it for deletion is safe even without a delete_empty callback. Classifiers without one (the check marks the proto unconditionally) are rtnl-serialized, so the raced window this guard closes cannot arise for them.
This is a follow-up to commit d4e359b3608a ("net/sched: cls_api: fix teardown of an adopted proto on insert-race loss"), which stopped the loser of the insert race from unlinking the winner's live proto but left the empty-proto residual in place.
Conditions to recreate:
tc filter add dev veth0 ingress protocol ip pref 1 flower skip_sw ... action drop (both fail in fl_hw_replace_filter
after publishing their handle in the idr); repeat in a loopfilter protocol ip pref 1 flower chain 0 header in
tc filter show with no filter entriesThis page as .md · .json · in your agent: get_signal("CVE-2026-98811")
NVD data is provided by NIST and is public domain. Posts quoted belong to their authors.