Live › vulnerability › CVE-2026-98629
Go to dashboardThe Linux kernel's traffic-control u32 classifier mishandles IDR keys for manually created hash tables, so deleting one can leak its entry or drop an unrelated live table's entry. A later auto-allocated handle can then alias a live manual table and misroute lookups, and an unprivileged local attacker is not stated in the sources.
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 running a Linux kernel with the net/sched cls_u32 classifier in use, particularly hosts that create tc u32 filters with explicit divisor handles on a qdisc. Hosts that do not use tc u32 filters are unlikely to be exposed; the sources do not say whether unprivileged users can trigger it.
No product ranges from the sources yet.
uname -r and compare against the fixed kernel in your distribution's advisory (unknown from these sources).tc -d filter show dev <iface> ingress and look for u32 divisor entries with explicit handles like fh 801:.Each 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_u32: fix manual hash table handle IDR aliasing
A u32 hash table created with an explicit handle ('tc filter add ... handle 801: u32 divisor N') keys its IDR entry on the raw handle, while the destroy paths free it under handle2id(handle). The two key domains disagree for handles in the 0x800..0xFFF htid range: handle2id() folds them back into the auto-allocated id space (1..0x7FF).
A manual table therefore leaves its raw-keyed IDR entry unreachable on delete (a permanent leak), and its delete can drop the idr entry of an unrelated live auto table. A later auto allocation can then hand out a handle that aliases the live manual table; u32_lookup_ht() first-match routes lookups and TCA_U32_LINK for that htid to the wrong table.
Key the divisor-path alloc on handle2id(handle) so allocation and removal share one key domain. A manual handle that maps onto an id already in use is rejected with -ENOSPC, and auto allocation skips ids held by live manual tables.
Conditions to recreate:
ip link add test0 type dummy
tc qdisc add dev test0 clsact
tc filter add dev test0 ingress protocol ip pref 1
handle 801: u32 divisor 16
tc filter add dev test0 ingress protocol ip pref 2 u32 divisor 16
tc -d filter show dev test0 ingress | grep 'fh 801:'
Also tested with a poc with a live u32 table on the block, add/delete a manual table 'handle 901: u32 divisor 1' twice; unpatched, the re-add fails with -ENOSPC because the raw key leaked on the first delete.
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