* [CVE-2026-98793][MODERATE REGULAR] netfilter: bpf: reject invalid NAT manipulation types [ Upstream
@ 2026-10-24 15:01 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-24 15:01 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98793
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: bpf: reject invalid NAT manipulation types [ Upstream
Commit: ea777dc90ab37e64fa4b92f6fcf3b5edcef5e058
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ea777dc90ab37e64fa4b92f6fcf3b5edcef5e058
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98793
Analysis date: Sat, 24 Oct 2026 11:01:50 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
Invalid BPF NAT manipulation values can leave live conntrack NAT state inconsistent and later crash privileged netfilter cleanup when it unlinks an uninitialized hlist node.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98793 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98793
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-2026-98793 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98793 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 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:N/I:N/A:H';*CWE-20;CWE-1284;CWE-824;**CWE-476;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'An unchecked NAT manipulation value passed through bpf_ct_set_nat_info can reach nf_nat_setup_info and trigger a WARN. With panic_on_warn enabled this can immediately panic the kernel. Otherwise NAT initialization can be marked complete without linking nat_bysource, and conntrack cleanup may attempt to unlink an uninitialized hlist node and crash the kernel. AV:L applies because triggering requires local BPF program execution rather than receipt of network packets. AC:L applies because an invalid manip value can be passed directly and no race is required. For the CVSS the PR:H value reflects that reliable triggering normally requires permission to load and attach a BPF program that can call this netfilter kfunc. For the CVSS the PR:L value in the paranoid vector covers deployments that delegate BPF loading through restricted capabilities, BPF tokens, containers, or management services. UI:N applies because no separate user action is needed, and S:U applies because the failure remains in the host kernel security authority. Availability impact is high through a kernel panic or cleanup crash. No controlled UAF, OOB access, information disclosure, or arbitrary write is established, so confidentiality and integrity remain none. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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 V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 1 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 Borderline / manual review recommended (with actual score 3) MAYBE REMOTE BPF SIMPLEFIX NETFILTER LINUS IPV6 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_B
RealUAF=NO
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: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; no floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +1 weak/indirect active-state corruption: attacker-selected `manip` causes `IPS_SRC_NAT_DONE` to be set while `nat_bysource` remains uninitialized, creating inconsistent live conntrack state.
* +1 reliable kernel crash/strong DoS: `panic_on_warn` can panic immediately; otherwise conntrack cleanup attempts to unlink the uninitialized hlist node. These are one availability signal, not two.
* Paranoid +1 active-state/trust-boundary review: attacker-shaped conntrack state is later consumed by privileged netfilter cleanup, while delegated BPF/container/namespace reachability remains credible but unresolved.
* No UAF, OOB write, controlled reclaim, arbitrary write, disclosure, authorization bypass, or LPE is shown.
* The hlist cleanup is not proven to complete a useful memory write before faulting; no separate integrity or extra availability point is awarded.
3. Reachability analysis
The caller must execute a BPF program able to invoke the netfilter kfunc and supply the invalid manipulation value. Normal deployments likely privilege BPF loading and attachment, but the supplied patch does not establish whether host-admin authority is mandatory or whether BPF tokens, delegated capabilities, or namespace-controlled networking provide the complete trigger. Therefore both host-admin and namespace-scoped privilege remain unknown. No race, special hardware, or remote-packet-only trigger is involved.
4. Primitive and severity reading
The primitive is attacker-influenced corruption of active conntrack/NAT bookkeeping: a completion flag is installed without the corresponding list initialization. Privileged cleanup later consumes that inconsistent structured state. This is CLASS_B active-state corruption, not a real UAF and not a proven controlled list-write primitive.
The shown outcome is WARN/panic or cleanup crash. Non-crash exploitation is unproven. Nevertheless, the write, later privileged consumer, and credible but unresolved delegated BPF or namespace boundary require Important-vs-Moderate review under the active-state trust-boundary rule. Thus `ImportantCandidate=YES` and automatic downgrade is disallowed without asserting Important severity.
5. One-sentence report phrase
Invalid BPF NAT manipulation values can leave live conntrack NAT state inconsistent and later crash privileged netfilter cleanup when it unlinks an uninitialized hlist node.
6. Manual review advice
MANUAL CHECK REQUIRED
Confirm the complete BPF load/attach/kfunc privilege chain and whether delegated or namespace-scoped actors can drive the corrupted conntrack object into host cleanup.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: netfilter: bpf: reject invalid NAT manipulation types [ Upstream
Commit: ea777dc90ab37e64fa4b92f6fcf3b5edcef5e058
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ea777dc90ab37e64fa4b92f6fcf3b5edcef5e058
Changed files:
net/netfilter/nf_nat_bpf.c
net/netfilter/nf_nat_core.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=ea777dc90ab37e64fa4b92f6fcf3b5edcef5e058
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98793 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98793
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:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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: 2
Paranoid ActionableScore: 3
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
^ permalink raw reply [relevance 21%]
Results 1-1 of 1 | reverse | sort options + mbox downloads above
-- links below jump to the message on this page --
2026-10-24 15:01 21% [CVE-2026-98793][MODERATE REGULAR] netfilter: bpf: reject invalid NAT manipulation types [ Upstream AL-KERNEL
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox