* [CVE-2026-90071][MODERATE 7.0] net/sched: sch_teql: restore skb->dev on the slave failure path [ Upstream
@ 2026-09-18 0:21 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-18 0:21 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90071
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net/sched: sch_teql: restore skb->dev on the slave failure path [ Upstream
Commit: 1360bc93f5be1be3cf937ebea667b3418dd30a79
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1360bc93f5be1be3cf937ebea667b3418dd30a79
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90071
Analysis date: Thu, 17 Sep 2026 20:21:07 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90071 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90071
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: MODERATE 7.0
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-90071 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90071 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A stale skb dev pointer can remain after a TEQL slave transmit failure because teql_master_xmit continues to the next slave without restoring the master device. If the packet is queued for an unresolved neighbour, the stale pointer does not hold a net_device reference and the previous slave can be freed while the packet remains in the ARP queue. Later timeout handling or resumed transmission can dereference the freed net_device, producing a confirmed use after free and a kernel crash. For the CVSS the PR:L value is used in the paranoid assessment because delegated CAP_NET_ADMIN, container root, or control of a network namespace may be sufficient to configure TEQL and remove a slave without full host administration. AC:H applies because exploitation requires a failed slave transmission, an unresolved neighbour, queued packet lifetime, and device deletion in the required order. The issue is not considered directly network reachable because remote traffic alone does not normally provide control over TEQL configuration or slave deletion. Impact is at least local denial of service and the confirmed net_device use after free may potentially affect confidentiality and integrity if freed memory can be reused in a controllable way.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) SKIP CVE-2026-90071 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE READ LOCK DANGER NULLPTR UAF NETWORK SKB HARDWARE KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* Applied conservative REAL UAF FLOOR 5: 4 -> 5. The stale active net_device is used in nontrivial asynchronous network processing, and the attacker controlling the device lifecycle can drive deletion while the skb remains queued.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2 Real UAF. skb->dev retains a non-reference-counted pointer to a slave net_device after transmission failure. The device is freed while the skb remains in arp_queue and is subsequently dereferenced.
* +1 Reliable kernel crash or strong DoS. KASAN confirms a slab-use-after-free read in __icmp_send, and the ordinary result without KASAN can be an Oops or kernel crash.
* +1 Attacker-influenced active-object lifetime. The triggering actor creates or configures the TEQL topology, drives packet queuing, and deletes the slave whose stale pointer remains in the skb. Device deletion is directly relevant to the vulnerable lifetime transition.
* Raw conservative total: 2 + 1 + 1 = 4.
* REAL UAF FLOOR 5 applies because this is an active structured net_device escaping into asynchronous neighbour processing, not a shallow destructor-only dereference.
Paranoid-only signal:
* +1 Structured stale-object exploitation leverage. The alternative post-free path can pass the stale net_device into neigh_direct_output and dev_queue_xmit, where operational net_device state is consumed. An actor with the same rtnetlink lifecycle control can influence net_device allocation and deletion, although controlled reclaim is not demonstrated.
* Raw paranoid total: 2 + 1 + 1 + 1 = 5.
* No paranoid floor or cap changes the score.
Important non-awarded signals:
* +2 Strong exploitation leverage not awarded. Controlled reclaim, attacker-shaped replacement contents, directed kernel read or write, callback control, and refcount takeover are not demonstrated.
* Remote reachability +2 not awarded. Network traffic can help queue the skb, but remote traffic alone does not establish control over TEQL configuration and slave deletion.
* Local unprivileged trigger +1 not awarded. The supplied reproducer runs as UID 0, and complete below-host-admin reachability is unresolved.
* No repeated release or refcount point. The first device release frees the net_device, but the later operation is a stale dereference rather than a second put, release, free, or refcount mutation on the same reference.
* No race penalty. The vulnerability requires an asynchronous sequence, but the evidence does not establish a narrow, one-shot, or externally uncontrollable timing window.
* No niche-subsystem penalty. TEQL is specialized, but rarity and attacker inability to instantiate it are not established.
* No additional Availability point. It would duplicate the same UAF-induced crash.
* No Confidentiality or Integrity points. No disclosure, controlled replacement, or modification primitive is demonstrated.
Repeated-release checks:
* First release can end lifetime: yes. netdev deletion reaches device_release and frees the allocation.
* Exact stale reference survives: yes. skb->dev remains stored in the queued skb.
* Second operation mutates lifetime or refcount: no. It dereferences or passes the stale object into network processing.
* Concrete repeated release or refcount +1: not awarded.
* Paranoid repeated-refcount leverage +1: not awarded.
* FLOOR 5: applied for active structured post-lifetime processing, not for repeated release.
3. Reachability analysis
The demonstrated sequence uses rtnetlink to create and delete net_device objects, configures a TEQL master and slaves, causes a slave transmission failure, queues the skb for an unresolved neighbour, and deletes the previous slave before timeout or resolution processing consumes the skb.
The trace identifies UID 0, but it does not establish that init-user-namespace host administration is mandatory. Network-device and qdisc operations commonly involve CAP_NET_ADMIN, but the supplied evidence does not resolve which user namespace governs every required TEQL creation, attachment, deletion, and trigger operation. Therefore HostAdminRequired and NamespaceScopedPrivilege remain UNKNOWN. No privilege penalty is applied from uncertainty.
A network namespace alone would not prove below-host-admin reachability. Complete namespace-scoped triggering would require evidence that an attacker can create the relevant namespace, obtain CAP_NET_ADMIN there, instantiate or access the TEQL master, configure all slaves, and delete the affected device without host-side setup.
No special physical hardware is required because the report reproduces the issue under QEMU. Kernel configuration or module availability is a prerequisite, but no separate host-provisioning requirement beyond availability of sch_teql is conclusively established.
The sequence is repeatable for an actor controlling the topology and packet flow. It is asynchronous, but the evidence does not establish a genuinely hard race deserving a timing penalty.
4. Primitive and severity interpretation
The exact primitive is an actual stale post-lifetime pointer to an active structured net_device. The pointer escapes in skb->dev into arp_queue without holding a device reference. After rtnetlink deletion frees the slave, neighbour timeout or resolution processing reads the freed object.
This is broader than an ordinary cleanup or destructor-only UAF. The stale pointer is consumed during active IPv4 error handling or packet transmission. Nevertheless, the demonstrated primitive is currently a post-free read leading to a crash. The patch does not establish controlled reclamation, arbitrary kernel read or write, callback hijacking, information disclosure, or privilege escalation.
There is no concrete repeated release or refcount mutation. Device deletion performs the lifetime-ending operation, while the later path dereferences the stale pointer rather than releasing it again.
PrimitiveClass is CLASS_B because a real active-object lifetime violation is confirmed and exploitation-leverage analysis remains necessary. It is not CLASS_A because no controlled replacement, directed corruption, or other strong exploitation primitive is established.
ImportantCandidate is YES because the stale active object escapes into asynchronous packet-processing paths, including a possible dev_queue_xmit path, while the actor controlling network-device lifecycle can influence the vulnerable transition. This creates meaningful Important-vs-Moderate uncertainty beyond an immediate cleanup fault.
AutoDowngradeAllowed is NO because automatically treating the issue as ordinary crash-only Moderate would discard unresolved leverage from an active net_device UAF. This does not itself prove Important severity. The operationally demonstrated impact remains local kernel DoS, while stronger confidentiality, integrity, or privilege-escalation consequences remain speculative.
5. One-sentence report phrase
A failed TEQL slave transmission can leave a queued skb holding a stale net_device pointer, allowing later neighbour timeout or transmit processing to dereference the freed device and crash the kernel, with broader active-object UAF leverage requiring manual review.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The confirmed active net_device UAF escapes into asynchronous network processing, and the dev_queue_xmit path leaves meaningful post-reuse behavior unresolved even though controlled reclaim or privilege escalation is not demonstrated.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: net/sched: sch_teql: restore skb->dev on the slave failure path [ Upstream
Commit: 1360bc93f5be1be3cf937ebea667b3418dd30a79
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1360bc93f5be1be3cf937ebea667b3418dd30a79
Changed files:
net/ipv4/icmp.c
lib/dump_stack.c
mm/kasan/report.c
include/asm-generic/qrwlock.h
net/ipv4/route.c
include/linux/skbuff.h
include/linux/instrumented.h
include/linux/atomic/atomic-instrumented.h
include/linux/rwlock_api_smp.h
kernel/locking/spinlock.c
include/net/dst.h
net/ipv4/arp.c
net/core/neighbour.c
mm/kasan/common.c
include/linux/kasan.h
mm/slub.c
net/core/dev.c
net/core/rtnetlink.c
mm/kasan/generic.c
drivers/base/core.c
lib/kobject.c
include/linux/kref.h
include/linux/rtnetlink.h
net/sched/sch_teql.c
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1360bc93f5be1be3cf937ebea667b3418dd30a79
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90071 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90071
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: unknown
Paranoid ActionableScore: 5
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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