* [CVE-2026-98441][MODERATE 7.0] net/sched: act_ct: avoid modifying shared unconfirmed ct entry [ Upstream
@ 2026-10-24 7:41 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 7:41 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98441
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net/sched: act_ct: avoid modifying shared unconfirmed ct entry [ Upstream
Commit: 2b783c562c3238ff50c34fd7a72a735c9cc73d9a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2b783c562c3238ff50c34fd7a72a735c9cc73d9a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98441
Analysis date: Sat, 24 Oct 2026 03:41:37 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
Shared unconfirmed conntrack extension reallocation can leave an expectation-list pointer stale and cause a later destruction-path UAF under an unusual attacker-influenced act_ct clone sequence.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98441 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98441
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-2026-98441 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98441 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) 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-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'act_ct can modify a shared unconfirmed conntrack entry when cloned skbs are processed again with different extension requirements. Helper setup can place an extension pointer in an expectation list, while a later commit, label, or NAT operation on another clone can reallocate the extension area and leave a stale pointer that is used during destruction, producing a kernel UAF. Triggering requires an unusual same zone traffic control pipeline, processing of both clones, and a suitable failed confirmation ordering. For the CVSS the PR:H base value reflects the usual need for CAP_NET_ADMIN to create the required tc act_ct and cloning pipeline. For the CVSS the PR:L paranoid value covers delegated network administration in a namespace or service account, while AC:H reflects the required ordering window. The demonstrated UAF supports strong availability impact and possible confidentiality or integrity impact, but no arbitrary write or proven privilege escalation exploit is established. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 7 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 KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE REMOTE DANGER UAF NETWORK SKB LINUS KPANIC PACKET DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - checked
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ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 4.
* Conservative score: 4; no floor or cap changed it.
* Raw paranoid score: 5.
* Paranoid score: 5; no floor or cap changed it.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 — Real UAF: modifying a shared, unconfirmed conntrack entry can reallocate extension storage, leaving the expectation-list extension pointer stale for later destruction.
* +1 — Reliable crash/strong DoS plausible from the documented destruction-path UAF; no separate availability point.
* +1 — Attacker-influenced active lifetime state: the configured clone/act_ct pipeline can repeatedly drive differing helper, label, or NAT extension requirements on the shared entry.
* Paranoid +1 — Structured stale-object leverage: the corrupted expectation-list pointer survives extension reallocation and is later consumed by resource-destruction processing. Exact destructor operations and reclaim behavior are not supplied, so this is not Class A.
* No race penalty: an unusual failed-confirmation ordering is required, but the evidence does not establish a narrow, uncontrollable, one-shot race.
* Not awarded: controlled reclaim, arbitrary/directed write, callback control, disclosure, C/I impact, LPE, or remote reachability.
3. Reachability analysis
The trigger requires an unusual tc act_ct cloning pipeline, shared same-zone unconfirmed conntrack state, differing extension requirements, and failed confirmation. CAP_NET_ADMIN is normally needed to configure tc, but the evidence does not resolve whether the complete clone, helper/NAT, and retry sequence requires host-admin authority or works with delegated/net-namespace CAP_NET_ADMIN. Thus both privilege fields remain UNKNOWN. No special hardware is required. Traffic can exercise an already configured pipeline, but ordinary unprivileged setup is not shown.
4. Primitive and severity reading
This is an active structured-object UAF, not fixed stale storage: extension reallocation invalidates a pointer already wired into an expectation list, and destruction later consumes it. The later use is cleanup-related, but it acts on corrupted lifetime-bearing structured state rather than merely detecting an invalid value. No repeated put/refcount operation on the exact same reference is shown.
The patch supports Class B lifetime corruption and plausible host crash. Controlled reuse or a useful non-crash write primitive remains unproven. ImportantCandidate is YES under the active-state/trust-boundary rule because attacker-influenced structured conntrack state reaches a privileged kernel destructor while the delegated-netns versus host boundary remains credible but unresolved. Auto-downgrade is therefore unsafe, although Important severity itself is not proven.
5. One-sentence report phrase
Shared unconfirmed conntrack extension reallocation can leave an expectation-list pointer stale and cause a later destruction-path UAF under an unusual attacker-influenced act_ct clone sequence.
6. Manual review advice
MANUAL CHECK REQUIRED
Confirm the destructor’s exact stale-pointer operations and whether delegated or namespace-scoped CAP_NET_ADMIN can complete the full trigger.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: net/sched: act_ct: avoid modifying shared unconfirmed ct entry [ Upstream
Commit: 2b783c562c3238ff50c34fd7a72a735c9cc73d9a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2b783c562c3238ff50c34fd7a72a735c9cc73d9a
Changed files:
net/sched/act_ct.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=2b783c562c3238ff50c34fd7a72a735c9cc73d9a
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98441 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98441
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:L/I:L/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: 4
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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