[CVE-2026-98584][MODERATE REGULAR] net/sched: fix potential stack infoleak in em_text_dump() [ Upstream

[CVE-2026-98584][MODERATE REGULAR] net/sched: fix potential stack infoleak in em_text_dump() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98584
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/sched: fix potential stack infoleak in em_text_dump() [ Upstream
Commit: 9923e1c537f91f3530b52d4efce85f3d9c131bf8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9923e1c537f91f3530b52d4efce85f3d9c131bf8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98584
Analysis date: Mon, 19 Oct 2026 01:53:15 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: YES

Summary:
`em_text_dump exposes uninitialized kernel stack bytes through RTM_GETTFILTER netlink responses, creating a limited local information disclosure that requires manual review for sensitive and repeatable contents.`

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98584 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98584

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 REGULAR
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-2026-98584	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98584 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, 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:N/A:N';*CWE-457;*CWE-200;CWE-908;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'em_text_dump can disclose uninitialized kernel stack bytes because a stack allocated tcf_em_text structure is only partially written before its full contents are copied into a netlink response. KMSAN confirmed the disclosure through tc filter show and a raw RTM_GETTFILTER dump, including uninitialized bytes left after the NUL terminator in the algorithm name field. For the CVSS the PR:L value is used because a local process must issue the netlink request, even if the relevant dump operation may be available to an otherwise unprivileged user on some systems. The base impact is C:L because the exposed bytes are limited and their sensitivity is not established. The paranoid impact is C:H because repeated dumps may disclose kernel pointers or other sensitive stack remnants that could assist a later attack. No direct integrity or availability impact is established because the primitive is an uninitialized stack read rather than memory corruption. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 5.5 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	REMOTE KASAN LEAK NETWORK LINUS TEST  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Local unprivileged trigger. RTM_GETTFILTER dump requests are GET operations and normally do not require CAP_NET_ADMIN, although a matching em_text filter must already exist.
* +1 Confidentiality plausible. KMSAN directly confirms that 12 uninitialized kernel-stack bytes are copied into a userspace-visible netlink response.
* +0 Strong or substantial disclosure. The leaked bytes may contain sensitive stack remnants, but stable pointers, credentials, keys, or another specific protected value are not demonstrated.
* +0 Practical exploit chain. Repeated dumps are possible, but no KASLR bypass, privilege escalation, or protected-resource access chain is established.
* +0 Integrity and availability. The operation only discloses uninitialized bytes. It does not write outside the object, corrupt kernel state, or cause a demonstrated crash.
* +0 B5-R, B3-PENDING, V32, V33, and V34. There is no OOB write, shared-backing write, checksum metadata corruption, or privileged downstream corruption consumer.
* +0 B4-PENDING. No authorization guard changes from DENY to ALLOW.

No negative points were applied. The requirement for an existing em_text rule limits exposure but does not prove that the querying attacker needs host-admin privilege.

3. Reachability analysis

A local process can issue `tc filter show` or a raw RTM_GETTFILTER dump and receive the affected netlink response. Numeric UID 0 and host-administrator powers are not required for the dump operation.

Creating the em_text filter normally requires CAP_NET_ADMIN, so exploitation against an existing host namespace depends on prior configuration by an administrator or network-management service. The attacker does not need to be the actor that created that filter. Whether an attacker can instantiate the complete setup inside an attacker-created user and network namespace depends on namespace policy, so NamespaceScopedPrivilege remains UNKNOWN.

There is no remote packet-triggered path. No special hardware, race, retry sequence, or timing window is required.

4. Primitive and severity interpretation

The exact primitive is a confirmed disclosure of uninitialized stack contents. `strscpy()` writes the algorithm name and NUL terminator but does not initialize the remaining bytes of `conf.algo`. `nla_put_nohdr()` then copies the complete `tcf_em_text` structure into the netlink response.

This is CLASS_B because a real userspace-visible kernel information-disclosure primitive exists, but it is limited and does not qualify as substantial CLASS_A disclosure on the supplied evidence. It is not a UAF, OOB read beyond the stack object, OOB write, authorization bypass, or memory-corruption primitive.

The demonstrated consequence is disclosure of 12 uninitialized bytes per affected dump. Sensitive kernel pointers or other useful remnants are technically possible, but their presence and stability are unresolved. ImportantCandidate is therefore NO. Manual review remains required to determine production-kernel contents and repeatability. AutoDowngradeAllowed is YES because no Important-preserving corruption, ownership, authorization, or boundary-bypass primitive is established.

5. One-sentence report phrase

`em_text_dump exposes uninitialized kernel stack bytes through RTM_GETTFILTER netlink responses, creating a limited local information disclosure that requires manual review for sensitive and repeatable contents.`

6. Manual review recommendation

MANUAL CHECK REQUIRED

Verify whether repeated dumps disclose stable kernel pointers or other sensitive values on production builds and whether affected em_text filters are present in relevant namespaces.

7. Call-site confidence

Call-site confidence: high

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

Patch: net/sched: fix potential stack infoleak in em_text_dump() [ Upstream
Commit: 9923e1c537f91f3530b52d4efce85f3d9c131bf8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9923e1c537f91f3530b52d4efce85f3d9c131bf8

Changed files:
  net/sched/em_text.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=9923e1c537f91f3530b52d4efce85f3d9c131bf8

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

The original Linux kernel CVE announcement for CVE-2026-98584 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98584

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:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 5.5

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

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).