CVE-2026-23074

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

net/sched: Enforce that teql can only be used as root qdisc

Design intent of teql is that it is only supposed to be used as root qdisc.

We need to check for that constraint.

Although not important, I will describe the scenario that unearthed this

issue for the curious.

GangMin Kim <[email protected]> managed to concot a scenario as follows:

ROOT qdisc 1:0 (QFQ)

├── class 1:1 (weight=15, lmax=16384) netem with delay 6.4s

└── class 1:2 (weight=1, lmax=1514) teql

GangMin sends a packet which is enqueued to 1:1 (netem).

Any invocation of dequeue by QFQ from this class will not return a packet

until after 6.4s. In the meantime, a second packet is sent and it lands on

1:2. teql's enqueue will return success and this will activate class 1:2.

Main issue is that teql only updates the parent visible qlen (sch->q.qlen)

at dequeue. Since QFQ will only call dequeue if peek succeeds (and teql's

peek always returns NULL)

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References