--- id: CVE-2026-23074 title: |- 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 const… summary: |- 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 const… severity: high cvss: 7.8 cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H' cwe: - CWE-416 - CWE-825 vendor: linux product: linux_kernel affected: - 'linux_kernel >= 2.6.12.1, < 5.10.249' - 'linux_kernel >= 5.11, < 5.15.199' - 'linux_kernel >= 5.16, < 6.1.162' - 'linux_kernel >= 6.2, < 6.6.122' - 'linux_kernel >= 6.7, < 6.12.68' - 'linux_kernel >= 6.13, < 6.18.8' - linux_kernel = 2.6.12 - linux_kernel = 6.19 patched: - linux_kernel 6.18.8 published: '2026-02-04' updated: '2026-06-30' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-23074' references: - url: 'https://git.kernel.org/stable/c/0686bedfed34155520f3f735cbf3210cb9044380' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/16ed73c1282d376b956bff23e5139add061767ba' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/4c7e8aa71c9232cba84c289b4b56cba80b280841' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/50da4b9d07a7a463e2cfb738f3ad4cff6b2c9c3b' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/73d970ff0eddd874a84c953387c7f4464b705fc6' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/ae810e6a8ac4fe25042e6825d2a401207a2e41fb' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/dad49a67c2d817bfec98e6e45121b351e3a0202c' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://access.redhat.com/errata/RHSA-2026:3083' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:3110' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:3268' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:3277' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:3360' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:3388' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:3634' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:3685' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:3810' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/security/cve/CVE-2026-23074' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2436791' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: >- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-23074.json label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://www.cve.org/CVERecord?id=CVE-2026-23074' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-23074' - url: >- https://lore.kernel.org/linux-cve-announce/2026020419-CVE-2026-23074-6bb8@gregkh/T tags: - nvd - cve.org - csaf - vex - red-hat epss: 0.00142 epssPercentile: 0.02877 ingestedAt: '2026-07-03T18:53:52.167Z' ssvc: exploitation: none automatable: 'no' technicalImpact: total timestamp: '2026-06-16T20:34:18.445688Z' scores: nvd: 7.8 vendor: 7 --- ## Overview 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 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. ## Affected - `linux_kernel >= 2.6.12.1, < 5.10.249` - `linux_kernel >= 5.11, < 5.15.199` - `linux_kernel >= 5.16, < 6.1.162` - `linux_kernel >= 6.2, < 6.6.122` - `linux_kernel >= 6.7, < 6.12.68` - `linux_kernel >= 6.13, < 6.18.8` - `linux_kernel = 2.6.12` - `linux_kernel = 6.19` ## Remediation Upgrade past the affected range: - `linux_kernel 6.18.8` ## Vendor advisories - **RHSA-2026:3810** · Red Hat · fixed in: Red Hat Enterprise Linux Server -EXTENSION(v. 6 ELS-EXTENSION), Red Hat Enterprise Linux Server Optional -EXTENSION (v. 6 ELS -EXTENSION) · released 2026-03-05 · [advisory](https://access.redhat.com/errata/RHSA-2026:3810) - **RHSA-2026:3685** · Red Hat · fixed in: Red Hat Enterprise Linux Server (v. 7 ELS), Red Hat Enterprise Linux Server Optional (v. 7 ELS) · released 2026-03-03 · [advisory](https://access.redhat.com/errata/RHSA-2026:3685) - **RHSA-2026:3634** · Red Hat · fixed in: Red Hat Enterprise Linux for Real Time (v. 7 ELS) · released 2026-03-03 · [advisory](https://access.redhat.com/errata/RHSA-2026:3634) - **RHSA-2026:3083** · Red Hat · fixed in: Red Hat Enterprise Linux BaseOS (v. 8), Red Hat Enterprise Linux CRB (v. 8) · released 2026-02-23 · [advisory](https://access.redhat.com/errata/RHSA-2026:3083) - **RHSA-2026:3388** · Red Hat · fixed in: Red Hat Enterprise Linux BaseOS AUS (v. 8.2) · released 2026-02-26 · [advisory](https://access.redhat.com/errata/RHSA-2026:3388) - **RHSA-2026:3360** · Red Hat · fixed in: Red Hat Enterprise Linux BaseOS AUS (v.8.4), Red Hat Enterprise Linux BaseOS EUS EXTENSION (v.8.4) · released 2026-02-25 · [advisory](https://access.redhat.com/errata/RHSA-2026:3360) - **RHSA-2026:3268** · Red Hat · fixed in: Red Hat Enterprise Linux BaseOS AUS (v.8.6), Red Hat Enterprise Linux BaseOS E4S (v.8.6), Red Hat Enterprise Linux BaseOS TUS (v.8.6) · released 2026-02-25 · [advisory](https://access.redhat.com/errata/RHSA-2026:3268) - **RHSA-2026:3277** · Red Hat · fixed in: Red Hat Enterprise Linux BaseOS E4S (v.8.8), Red Hat Enterprise Linux BaseOS TUS (v.8.8) · released 2026-02-25 · [advisory](https://access.redhat.com/errata/RHSA-2026:3277) - **RHSA-2026:3110** · Red Hat · fixed in: Red Hat Enterprise Linux NFV (v. 8), Red Hat Enterprise Linux RT (v. 8) · released 2026-02-23 · [advisory](https://access.redhat.com/errata/RHSA-2026:3110)