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Linux Kernel EUVDEUVD-2026-59414

| CVE-2026-74267 CRITICAL
2026-08-15 Linux GHSA-f72g-gj5h-9p7f
Information Disclosure Linux Canonical
Critical
Disputed · 9.8 Vendor: Linux
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Obtain CAP_NET_ADMIN (local/namespace)
  2. Delivery
    Configure qfq qdisc with codel child via tc
  3. Exploit
    Drive traffic triggering codel drop during peek
  4. Execution
    Premature qlen_notify deactivates qfq class
  5. Persist
    Reset/destroy qdisc dereferences freed node
  6. Impact
    Kernel GPF / denial of service

Vulnerability Assessment

Exploitation Conditions

Exploitation requires the ability to configure Linux traffic control qdiscs, i.e., CAP_NET_ADMIN in the target network namespace (obtainable via root or an unprivileged user namespace where permitted). The specific trigger is a nested qdisc hierarchy with sch_codel installed as a child of sch_qfq, exercised so that codel drops a packet during the peek operation at the moment its qlen would transiently read zero. Limiting factors: this is local, not remote - the CVSS AV:N/PR:N metrics overstate reach; the sch_codel and sch_qfq modules must be present/loaded; and non-default qdisc configurations must be created by the attacker. Systems that deny CAP_NET_ADMIN to untrusted users and disable unprivileged user namespaces are not exploitable by unprivileged actors.
Impact

The published CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N ... 9.8 Critical) is inconsistent with the actual defect and should not drive prioritization. Creating, grafting, or manipulating tc qdiscs (attaching codel under qfq and driving the peek path) requires CAP_NET_ADMIN in the relevant network namespace - i.e., local privileged access, not remote unauthenticated network reach. The realistic impact is a kernel crash (denial of service) via wild-memory access; while memory corruption can theoretically be shaped further, no such escalation is demonstrated. Corroborating lower-risk signals: EPSS is only 0.21% (12th percentile), the CVE is not in CISA KEV, and no POC beyond the reproducer implied by the KASAN trace is published. The input tag 'Information Disclosure' is not supported by the description, which describes a use-after-free/GPF (DoS/memory corruption), not an info leak - treat that tag as unreliable. Net assessment: genuine kernel bug worth patching in fleet hygiene, but real-world risk is far below the 9.8 score - CVSS network/no-privilege metrics contradict the config-dependent, locally-privileged nature of the flaw; verify against your patch baseline rather than the raw score.
Exploit ScenarioDerived

A local user with CAP_NET_ADMIN (for example, root inside a container granted network admin, or a process in an unprivileged user namespace) uses the tc utility to build a qfq qdisc with a codel child, then drives traffic so codel drops packets during a peek while its queue length is 1. The premature qlen_notify deactivates the qfq aggregate, and a subsequent qdisc reset/destroy dereferences the freed list node, crashing the kernel (general protection fault). No public exploit is identified beyond the reproducer implied by the KASAN report; the low CVSS attack complexity reflects that the trigger is a deterministic tc configuration sequence.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.2% exploitation probability (EPSS)

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AnalysisAIv1 – Aug 17, 2026

Memory corruption in the Linux kernel network scheduler (net/sched/sch_codel) allows a privileged local user to trigger a wild/dangling pointer dereference by mis-accounting queue length during the CoDel peek operation. When CoDel drops packets during peek it calls qdisc_tree_reduce_backlog before re-incrementing qlen; if qlen momentarily hits zero while peek still returns an skb, the parent qdisc's qlen_notify prematurely deactivates the class, corrupting scheduler state (demonstrated as a KASAN wild-memory-access in qfq_deactivate_agg when qfq parents a codel child). No public exploit identified at time of analysis; EPSS is low (0.21%, 12th percentile) and this is not in CISA KEV.

RemediationAI

Vendor-released patch: update to a fixed stable release for your branch - 6.12.97, 6.6.145, 6.1.178, 5.15.212, 5.10.261, or 6.18.40 (mainline fixed in 6.15/7.1.5/7.2-rc1) - the corresponding commits are on the kernel.org stable tree (https://git.kernel.org/stable/c/bb9cfd874ee884117b33e92a002b9a45b48202f4 and siblings). If immediate patching is not possible, the practical compensating control is to restrict who can configure traffic control: withhold CAP_NET_ADMIN from untrusted users and constrain unprivileged user namespaces (e.g., sysctl kernel.unprivileged_userns_clone=0 or user.max_user_namespaces=0), which prevents attackers from creating the qfq-over-codel qdisc hierarchy that triggers the fault; the trade-off is that container runtimes and network-management tooling relying on user namespaces or delegated CAP_NET_ADMIN may break. Avoiding codel-as-child-of-qfq configurations also sidesteps the specific crash path but is not a general fix. Apply the vendor patch as the durable remediation.

Affected VersionsENISA

Linux 6.12.24 <6.12.97
Linux 6.14.3 <6.15
Linux eda741fe155ddf5ecd2dd3bfbd4fc3c0c7dbb450 <7a05af7f58566682b73578b72ca8e53a268c43bd
Linux e73c838c80dccb9e4f19becc11d9f3cb4a27d483
Linux 4d55144b12e742404bb3f8fee6038bafbf45619d <e4615aa6bb7802944ae790cb4b3ef8c1b7491af3
Linux patch: 5.15.212
Linux 7a742a9506849d1c1aa71e36c89855ceddc7d58e
Linux patch: 5.10.261
Linux cc71a757da78dd4aa1b4a9b19cb011833730ccf2 <bb9cfd874ee884117b33e92a002b9a45b48202f4
Linux 342debc12183b51773b3345ba267e9263bdfaaef <755108bb7a5083e911294c416cfea605dc75632f
Linux a57fe60ef4cf96bfbb6b58397ec28bdb5a5c6b31
Linux patch: 7.1.5
Linux 6.6.88 <6.6.145
Linux 2f9761a94bae33d26e6a81b31b36e7d776d93dc1 <e8c6dbadf139cb14ea6ed14add6ed6e88504dedd
Linux 6.1.135 <6.1.178
Linux 5.15.190 <5.15.212
Linux patch: 6.1.178
Linux patch: 6.12.97
Linux 342debc12183b51773b3345ba267e9263bdfaaef <52f1da34c9f4d5bdc1e8b44242da5c7ba8db85f3
Linux 6.15
Linux 829c49b6b2ff45b043739168fd1245e4e1a91a30 <eba49fd85995a3851c597fa2d214f8d21736e1d8
Linux patch: 6.18.40
Linux patch: 6.6.145
Linux 5.10.241 <5.10.261
Linux 6.13.12 <6.14
Linux patch: 7.2-rc1
Linux 342debc12183b51773b3345ba267e9263bdfaaef <91e0a793a72374c20ab31a40ccec21373e82e973
Linux 5.4.297 <5.5
Linux patch: 0

Affected Packages

euvd linux fix: 5.5, 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, 6.14, 6.15

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

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Technical ContextAI · show details

The affected component is the Linux Traffic Control (tc) queueing discipline subsystem, specifically the Controlled Delay (CoDel) AQM qdisc used to combat bufferbloat. Qdiscs form a tree, and child qdiscs must notify parents of backlog/queue-length changes via qdisc_tree_reduce_backlog(), which can invoke the parent's qlen_notify() callback to activate/deactivate scheduling classes. The bug is an ordering/accounting error (root-cause class akin to CWE-416 use-after-free / improper state management, though the CVE lists CWE as N/A): the backlog reduction is reported before the child's qlen is restored, so the parent sees a transient zero queue length and deactivates a class that still holds a packet. When a Quick Fair Queueing (qfq) qdisc parents the codel qdisc, the stale/deactivated aggregate is later dereferenced (the 0xdead000000000122 poison pointer in the trace is a freed list-node), producing a general protection fault. CPE data identifies the affected product simply as cpe:2.3:a:linux:linux.

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Severity by source

Sources disagree (Medium–Critical)
Vendor (Linux) PRIMARY 9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
vuln.today AI 4.4 MEDIUM

Requires local CAP_NET_ADMIN to configure qdiscs (PR:H) via a deterministic tc sequence (AC:L); realistic impact is kernel crash (A:H) with no demonstrated C/I loss.

3.1 AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
4.0 AV:L/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE 7.1 HIGH
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
Red Hat 5.5 MEDIUM

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorVendor: Linux

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

4
CVSS changed
Aug 17, 2026 - 06:22 NVD
9.8 (CRITICAL)
Patch available
Aug 15, 2026 - 07:20 EUVD
CVE Published
Aug 15, 2026 - 05:57 cve.org
UNKNOWN (no severity yet)
CVE Published
Aug 15, 2026 - 05:57 cve.org
CRITICAL 9.8

DescriptionCVE.org

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

net/sched: sch_codel: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen

Whenever codel drops packets during peek, it calls qdisc_tree_reduce_backlog. An issue arises because it calls qdisc_tree_reduce_backlog before it reincrements the qlen. If qlen drops to zero, but peek returns an skb, the parent's qlen_notify callback will be executed even though codel still has 1 packet on the queue and, thus, will mistakenly deactivate the parent's class causing issues like a wild memory access when qfq has codel as a child:

[ 36.339843][ T370] Oops: general protection fault, probably for non-canonical address 0xfbd59c0000000024: 0000 [#1] SMP KASAN NOPTI [ 36.340408][ T370] KASAN: maybe wild-memory-access in range [0xdead000000000120-0xdead000000000127] [ 36.340737][ T370] CPU: 2 UID: 0 PID: 370 Comm: tc Not tainted 7.1.0-rc5-00287-g66e13b626592 #87 PREEMPT(full) [ 36.341113][ T370] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 36.341357][ T370] RIP: 0010:qfq_deactivate_agg (include/linux/list.h:1029 (discriminator 2) include/linux/list.h:1043 (discriminator 2) net/sched/sch_qfq.c:1369 (discriminator 2) net/sched/sch_qfq.c:1395 (discriminator 2)) sch_qfq [ 36.342221][ T370] RSP: 0018:ffff8881100ef370 EFLAGS: 00010216 [ 36.342422][ T370] RAX: 0000000000000000 RBX: ffff8881058a9568 RCX: dffffc0000000000 [ 36.342664][ T370] RDX: 1ffff11021064dc3 RSI: ffff888108326e00 RDI: dffffc0000000000 [ 36.342905][ T370] RBP: ffff8881058a8280 R08: dead000000000122 R09: 1bd5a00000000024 [ 36.343140][ T370] R10: fffffbfff2940329 R11: fffffbfff2940329 R12: 0000000000000000 [ 36.343383][ T370] R13: dead000000000100 R14: ffff8881058a9580 R15: ffff8881058a9578 [ 36.343631][ T370] FS: 00007fc04b0ca780(0000) GS:ffff888184fef000(0000) knlGS:0000000000000000 [ 36.343911][ T370] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 36.344116][ T370] CR2: 0000557c02c02000 CR3: 000000010e0ba000 CR4: 0000000000750ef0 [ 36.344359][ T370] PKRU: 55555554 [ 36.344481][ T370] Call Trace: ... [ 36.345054][ T370] qfq_reset_qdisc (net/sched/sch_qfq.c:357 net/sched/sch_qfq.c:1487) sch_qfq [ 36.345222][ T370] qdisc_reset (net/sched/sch_generic.c:1057) [ 36.345503][ T370] __qdisc_destroy (net/sched/sch_generic.c:1096) [ 36.345677][ T370] qdisc_graft (net/sched/sch_api.c:1062 net/sched/sch_api.c:1053 net/sched/sch_api.c:1159) [ 36.346335][ T370] tc_get_qdisc (net/sched/sch_api.c:1528 net/sched/sch_api.c:1556)

Fix this by only calling qdisc_tree_reduce_backlog in peek after the qlen is restored.

Executive ViewAI

Why It Matters

A critical memory corruption vulnerability in the Linux kernel network scheduler (CVE-2026-74267) could enable denial of service or corrupt kernel state, affecting system stability and security. Exploitation requires local user with privileged access; however, no public exploit identified at time of analysis and exploitation probability is minimal (EPSS 0.2%, not in CISA KEV). Organizations should prioritize patching systems where local users have elevated permissions, but can sequence remediation based on operational role and infrastructure risk.

Business Impact: High
Compensating Controls

Apply vendor patch. Interim: restrict local user access to systems until patched, and disable CoDel queue discipline (net.core.default_qdisc=pfifo) on unpatched systems if operationally feasible.

Threat Intelligence Overview

EPSS Score
0.2%
Top 88% exploitable
Prevalence
Ubiquitous
Linux kernel runs on the vast majority of servers and cloud hosts
Data Quality
5 sources
Confidence: Medium
EUVD NVD CVE.org EPSS Vendor

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity CRITICAL
CISA KEV No
Public POC No
EPSS 0.2%
Patch available Yes
Active threat No
Deciding rule
CRITICAL severity
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact
High

Priority Score

49
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +49
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Availability Extension 15 SP7 Affected
SUSE Linux Enterprise High Availability Extension 15 SP7 Affected
SUSE Linux Enterprise High Availability Extension 16.0 Affected

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-74267 ADVISORY https://ubuntu.com/security/notices/USN-8781-1 REF https://git.kernel.org/stable/c/52f1da34c9f4d5bdc1e8b44242da5c7ba8db85f3 REF https://git.kernel.org/stable/c/755108bb7a5083e911294c416cfea605dc75632f REF https://git.kernel.org/stable/c/7a05af7f58566682b73578b72ca8e53a268c43bd REF https://git.kernel.org/stable/c/91e0a793a72374c20ab31a40ccec21373e82e973 REF https://git.kernel.org/stable/c/bb9cfd874ee884117b33e92a002b9a45b48202f4 REF https://git.kernel.org/stable/c/e4615aa6bb7802944ae790cb4b3ef8c1b7491af3 REF https://git.kernel.org/stable/c/e8c6dbadf139cb14ea6ed14add6ed6e88504dedd REF https://git.kernel.org/stable/c/eba49fd85995a3851c597fa2d214f8d21736e1d8

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