[CVE-2026-98703][IMPORTANT] wifi: mac80211: minstrel_ht: validate fixed rate index

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98703
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: wifi: mac80211: minstrel_ht: validate fixed rate index
Commit: f8ab6ae1fa360b0191252677f41e781dcb0ffe6e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f8ab6ae1fa360b0191252677f41e781dcb0ffe6e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98703
Analysis date: Mon, 19 Oct 2026 01:35:06 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A root user can supply an invalid Minstrel HT fixed rate index that causes deterministic out-of-bounds updates to adjacent kernel memory, requiring manual review despite the absence of a demonstrated privilege boundary or arbitrary write.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98703 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98703

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: IMPORTANT
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98703	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-98703 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-129;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H';BEST CVSS score: '7.8';DESCR 'An unchecked fixed_rate_idx debugfs value can be copied into the Minstrel HT selected rate fields and later decoded into a group and rate index by minstrel_ht_set_rate(). A value such as 65535 selects entries far beyond minstrel_mcs_groups and mi groups rates, after which the invalid location is dereferenced and updated as minstrel_rate_stats. This provides a local indexed out-of-bounds write into adjacent kernel memory and can cause a kernel crash or potentially affect kernel integrity. The available write values appear constrained by rate control processing, so a fully arbitrary write is not established. For the CVSS the PR:L value in the paranoid score reflects deployments where debugfs or this writable attribute is exposed to a reduced privilege container, service account, or local user. The normal debugfs deployment is root restricted and therefore supports PR:H for the base score. The issue is not network reachable. Impact is at least local denial of service and may include privilege escalation because actual adjacent kernel memory corruption is present. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 7.8 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were TEMP_KPANIC_MERGE_IMPORTANT_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 2.7 and ActionableScore 0 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	REMOTE WRITE KASAN OOB DEBUGFS TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=YES
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 5
* Raw paranoid score: 1
* Paranoid score: 5
* Applied conservative manual-review safety floor: 1 -> 5 because a confirmed attacker-indexed kernel OOB write exists.
* Applied paranoid manual-review safety floor: 1 -> 5 for the same established corruption primitive. No speculative exploitation bonus was added.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Strong corruption primitive. An arbitrary debugfs value controls the group and rate indices, producing confirmed writes beyond `minstrel_mcs_groups[]` and `mi->groups[].rates[]` into adjacent kernel memory.
* +1 Realistic kernel crash or strong DoS. Updating a far out-of-range location as `struct minstrel_rate_stats` can corrupt kernel objects and cause a fault, although a panic is not directly demonstrated.
* -2 Full host-administrator privilege. The commit explicitly states that the attribute is reachable only through a root-only debugfs mount and is not a privilege boundary.
* No additional integrity point. The OOB write is already counted as the strong corruption primitive, and modification of a protected object across an independent authority boundary is not established.
* No confidentiality point. No disclosure or kernel read-back path is shown.
* No arbitrary-write or controlled-target bonus. The index influences the destination, but values written by rate-control processing are constrained.
* No remote-reachability bonus. Network traffic alone cannot set `fixed_rate_idx`.
* No UAF, reclaim, callback, credential modification, or demonstrated LPE.
* No extra availability point because the possible kernel crash is counted once.
* B5-R is not established. Retry counters are among the modified fields, but the invalid index does not accumulate across retries because of a missing reset.
* V33 is not established. The OOB write is real, but no specific corrupted adjacent object, privileged downstream consumer, or credible below-host-admin boundary is identified.
* B3-PENDING is not applicable because shared or file-backed storage is not involved.
* B4-PENDING is not applicable because no authorization decision changes from DENY to ALLOW.

3. Reachability analysis

The complete demonstrated trigger requires writing an invalid integer to the mac80211 Minstrel HT `fixed_rate_idx` debugfs attribute. The relevant debugfs hierarchy must exist, `CONFIG_MAC80211_DEBUGFS` must be enabled, and a compatible mac80211 interface using Minstrel HT must be present.

The commit positively characterizes the mount as root-only, so host administrator access is required for the supported trigger. Although the file itself was created with writable permission bits, no supplied evidence shows that an ordinary user, container, delegated service, or attacker-created namespace can traverse the debugfs mount and write it. The complete operation is therefore not established as namespace-scoped.

No race or special timing is required. Once the invalid value is installed, normal rate-statistics processing reaches the malformed indices. Wireless packets may cause later rate-control activity, but they do not independently provide control of the debugfs value, so this is not a network-triggerable vulnerability.

4. Primitive and severity interpretation

The exact primitive is an attacker-indexed heap or slab OOB write. For example, value `65535` selects group `4095` and rate index `15`, while the valid dimensions are 42 groups and 10 rates. The resulting address is dereferenced and updated as `struct minstrel_rate_stats`, corrupting adjacent kernel memory.

This is active memory corruption rather than a read-only bounds violation, warning-only issue, or passive bookkeeping error. It is CLASS_A because an attacker-supplied index directly selects an out-of-bounds write location. It is not an arbitrary write because the payload and exact field updates are constrained by Minstrel rate-control logic.

The demonstrated consequence is adjacent kernel-memory corruption, with a realistic possibility of kernel crash. Privilege escalation, confidentiality loss, and corruption of a named security-sensitive victim remain unresolved rather than proven. There is no UAF or repeated release operation.

`ImportantCandidate=YES` and `AutoDowngradeAllowed=NO` preserve the confirmed write primitive for human examination. This does not establish Important operational severity because the supported trigger already requires host-administrator access and crosses no demonstrated privilege boundary.

5. One-sentence report phrase

A root user can supply an invalid Minstrel HT fixed rate index that causes deterministic out-of-bounds updates to adjacent kernel memory, requiring manual review despite the absence of a demonstrated privilege boundary or arbitrary write.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch establishes a genuine attacker-indexed kernel OOB write, so adjacent-object layout, written values, and possible security-sensitive victims should be reviewed manually even though the documented interface is root-only.

7. Call-site confidence

Call-site confidence: high

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: wifi: mac80211: minstrel_ht: validate fixed rate index
Commit: f8ab6ae1fa360b0191252677f41e781dcb0ffe6e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f8ab6ae1fa360b0191252677f41e781dcb0ffe6e

Commit description:

The fixed_rate_idx debugfs file is a plain u32 attribute, so any value
can be written to it.  minstrel_ht_update_stats() then copies the value
into mi->max_tp_rate[] and mi->max_prob_rate, and
minstrel_ht_set_rate() uses MI_RATE_GROUP()/MI_RATE_IDX() to index
minstrel_mcs_groups[] (42 entries) and mi->groups[].rates[] (10 entries)
with it.

Writing e.g. 65535 selects group 4095 and rate index 15, far outside
both arrays.  The out-of-bounds entries are dereferenced and updated as
struct minstrel_rate_stats (retry counts, etc.), so the invalid index
corrupts adjacent kernel memory.  With CONFIG_UBSAN_BOUNDS the access is
reported as an array-index-out-of-bounds in minstrel_ht_set_rate().

Only a valid group/rate pair, or U32_MAX to disable fixed rate
processing, can be used safely, so reject any other value when the
debugfs file is written.

The file is only reachable through a root-only debugfs mount, so this is
not a privilege boundary.  The out-of-bounds access is still a bug that
must not be reachable through a writable debugfs attribute.

Fixes: 24f7580 ("minstrel_ht: fixed rate mode through debugfs")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: LLM
Signed-off-by: Yuqi Xu <xuyuqiabc@gmail.com>
Reviewed-by: Ren Wei <weir@nebusec.ai>
Link: https://patch.msgid.link/288e6f6d30dc82ff40da502755e6666982f6b735.1789798000.git.xuyuqiabc@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/mac80211/rc80211_minstrel_ht.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=f8ab6ae1fa360b0191252677f41e781dcb0ffe6e

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DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98703 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98703

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:H/UI:N/S:U/C:N/I:H/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: IMPORTANT
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): IMPORTANT

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).