* [CVE-2026-90086][LOW] xsk: honor XDP_TX_METADATA in zero-copy path [ Upstream
@ 2026-09-18 6:16 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 6:16 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90086
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xsk: honor XDP_TX_METADATA in zero-copy path [ Upstream
Commit: 53a5b262d706b572840cbe8feae392538077ee19
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=53a5b262d706b572840cbe8feae392538077ee19
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90086
Analysis date: Fri, 18 Sep 2026 02:16:02 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90086 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90086
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-90086 LOW https://www.kernelcve.org/list/?q=CVE-2026-90086 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L';*CWE-20;CWE-754;*CWE-664;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'AF_XDP zero-copy TX can read and act on TX metadata whenever the UMEM has metadata space even if the specific descriptor does not set XDP_TX_METADATA. A local process that controls AF_XDP TX descriptors can therefore cause the driver path to treat stale or unintended UMEM bytes as metadata, which may lead to unexpected TX offload state or unrequested timestamp handling. For the CVSS the PR:L is used because triggering requires a local process with access to AF_XDP zero-copy TX and descriptor submission, often through delegated network privileges or a process already allowed to use the interface. The issue is not directly network reachable because remote packets do not control the local TX descriptor options. Impact appears limited to integrity of TX metadata handling and possibly local TX path availability. It does not show a kernel memory corruption primitive or a direct privilege escalation path.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES REMOTE OOB NETWORK DMAorINTERRUPT MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1. No floor or cap applied.
* Raw paranoid score: 2
* Paranoid score: 2. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 conservative: AF_XDP zero-copy TX metadata handling used metadata whenever UMEM had metadata space, even when the descriptor did not set XDP_TX_METADATA. This is a concrete input validation and state-consistency bug.
* +1 paranoid: limited local integrity or availability concern is plausible because stale or unintended UMEM metadata may influence TX offload state or unrequested timestamp handling.
* 0: Real UAF not awarded. The patch does not establish post-lifetime object use.
* 0: Strong semantic reinterpretation not awarded. The metadata affects TX metadata or offload handling, but no protected kernel object, ownership boundary, callback, pointer, or lifetime primitive is shown.
* 0: Controlled reclaim, arbitrary write, directed kernel write, kernel memory corruption, and privilege escalation are not demonstrated.
* 0: Remote reachability not awarded. Remote packets do not control local AF_XDP TX descriptor options.
* 0: Local unprivileged trigger not awarded. A local process can control descriptors only after AF_XDP zero-copy setup, but the complete privilege boundary for load, attach, and device setup is not established from the supplied input.
* 0: Extra availability not awarded. No kernel crash, panic, resource exhaustion, or host-wide DoS is established.
* 0: C/I security-boundary impact not awarded. The visible effect is incorrect metadata interpretation in the local TX path, not unauthorized access to another security principal.
3. Reachability analysis
Triggering requires a local process that can submit AF_XDP zero-copy TX descriptors and use a UMEM with TX metadata space. The attacker controls descriptor address and options, and the bug is that metadata is read even when the descriptor option XDP_TX_METADATA is absent.
For BPF/XDP, the complete path may involve XDP program loading or attachment, netdevice queue setup, and AF_XDP zero-copy enablement. The supplied input does not prove that all these stages are reachable by an ordinary unprivileged user, and it also does not prove that host-admin-equivalent privilege is always required. Therefore HostAdminRequired is UNKNOWN and NamespaceScopedPrivilege is UNKNOWN.
There is no direct network trigger. This is a local data-plane API issue, not a packet-processing vulnerability reachable from remote traffic. No special race is required. Hardware or driver dependence exists for affected zero-copy TX paths, but the issue is not scored as rare hardware because AF_XDP support across the listed drivers is normal enough and no physical-only prerequisite is established.
4. Primitive and severity interpretation
The exact primitive is an invalid metadata-state interpretation: the zero-copy TX path treats UMEM metadata as present based on pool metadata space rather than the per-descriptor XDP_TX_METADATA option.
This is not active kernel memory corruption. It is not a UAF, not an OOB access, not a repeated release/refcount bug, and not an authorization bypass. The mentioned unrequested timestamp overwrite appears to affect the metadata union associated with the userspace-visible metadata area, not an arbitrary kernel target.
PrimitiveClass is CLASS_C because the demonstrated behavior is invalid-state processing without an independently useful corruption primitive. Demonstrated consequence is incorrect TX metadata or offload handling. Speculative consequences beyond local TX behavior are not supported. ImportantCandidate is NO because there is no unresolved strong corruption, lifetime, ownership, or security-boundary primitive. AutoDowngradeAllowed is YES because the issue appears suitable for ordinary Moderate or Low-like handling unless a product-specific deployment gives untrusted tenants AF_XDP zero-copy TX access and relies on strict TX metadata isolation.
5. One-sentence report phrase
AF_XDP zero-copy TX could incorrectly consume UMEM TX metadata for descriptors that did not set XDP_TX_METADATA, allowing a local descriptor-submitting process to influence TX metadata or offload handling without evidence of kernel memory corruption or privilege escalation.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
Reason: no UAF, no kernel memory corruption, no authorization bypass, no remote trigger, and no demonstrated host-wide DoS or privilege escalation primitive are established by the supplied patch.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: xsk: honor XDP_TX_METADATA in zero-copy path [ Upstream
Commit: 53a5b262d706b572840cbe8feae392538077ee19
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=53a5b262d706b572840cbe8feae392538077ee19
Changed files:
drivers/net/ethernet/intel/igc/igc_main.c
drivers/net/ethernet/mellanox/mlx5/core/en/xsk/tx.c
drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
include/net/libeth/xsk.h
include/net/xdp_sock_drv.h
include/net/xsk_buff_pool.h
net/xdp/xsk_buff_pool.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=53a5b262d706b572840cbe8feae392538077ee19
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90086 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90086
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:L/PR:L/UI:N/S:U/C:N/I:L/A:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
The Best / paranoid CVSS score: 4.4
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: 1
Paranoid ActionableScore: 2
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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