Linux Kernel Teql UAF via nonroot qdisc misuse
CVE-2026-23074 Published on February 4, 2026
net/sched: Enforce that teql can only be used as root qdisc
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 <km.kim1503@gmail.com> 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), dequeue will never be called and thus the qlen
will remain as 0. With that in mind, when GangMin updates 1:2's lmax value,
the qfq_change_class calls qfq_deact_rm_from_agg. Since the child qdisc's
qlen was not incremented, qfq fails to deactivate the class, but still
frees its pointers from the aggregate. So when the first packet is
rescheduled after 6.4 seconds (netem's delay), a dangling pointer is
accessed causing GangMin's causing a UAF.
Products Associated with CVE-2026-23074
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Affected Versions
Linux:- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 73d970ff0eddd874a84c953387c7f4464b705fc6 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below ae810e6a8ac4fe25042e6825d2a401207a2e41fb is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below dad49a67c2d817bfec98e6e45121b351e3a0202c is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 0686bedfed34155520f3f735cbf3210cb9044380 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 4c7e8aa71c9232cba84c289b4b56cba80b280841 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 16ed73c1282d376b956bff23e5139add061767ba is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 50da4b9d07a7a463e2cfb738f3ad4cff6b2c9c3b is affected.
- Version 2.6.12 is affected.
- Before 2.6.12 is unaffected.
- Version 5.10.249, <= 5.10.* is unaffected.
- Version 5.15.199, <= 5.15.* is unaffected.
- Version 6.1.162, <= 6.1.* is unaffected.
- Version 6.6.122, <= 6.6.* is unaffected.
- Version 6.12.68, <= 6.12.* is unaffected.
- Version 6.18.8, <= 6.18.* is unaffected.
- Version 6.19, <= * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.