* [CVE-2026-98123][MODERATE 7.0] sctp: fix soft lockup from unpadded ASCONF-ACK parameter iteration [ Upstream
@ 2026-09-26 18:17 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-26 18:17 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98123
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: sctp: fix soft lockup from unpadded ASCONF-ACK parameter iteration [ Upstream
Commit: abf59d7f6fff23227256e8199aca5ade45758f8b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=abf59d7f6fff23227256e8199aca5ade45758f8b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98123
Analysis date: Sat, 26 Sep 2026 14:17:44 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98123 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98123
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-2026-98123 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98123 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-835;*CWE-20;CWE-125;**CWE-400;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'An inconsistency in SCTP ASCONF ACK parameter iteration can let a remote peer desynchronize verification from later parameter consumption. An odd length parameter can make sctp_get_asconf_response interpret attacker controlled bytes at a misaligned offset, and a decoded zero length can prevent the softirq loop from making progress. This can cause a CPU soft lockup and denial of service on a host with SCTP ADD IP enabled, an established association, and an outstanding ASCONF request. For the CVSS the PR:N value is used because a network peer can trigger the condition without local code execution or privileges on the target. The issue is remotely reachable over SCTP, although practical exposure depends on SCTP being permitted by network firewalls and on the required association state. A separate short ERR_CAUSE parameter can cause a bounded out of bounds read across the logical parameter boundary, but the read remains inside the received skb and does not provide a demonstrated kernel memory disclosure or write primitive. Impact is therefore denial of service without a supported privilege escalation path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) SKIP CVE-2026-98123 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE OOB DEADLOCK NETWORK LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 5.
* Conservative score: 5. No floor or cap applied.
* Raw paranoid score: 6.
* Paranoid score: 6. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2 Remote reachable. An SCTP peer can deliver the crafted ASCONF-ACK over the network once the affected ADD-IP association exists.
* +2 Strong attacker-influenced semantic reinterpretation. The verifier validates parameters using padded boundaries, while the consumer interprets the same bytes using unpadded boundaries. Attacker-controlled padding or adjacent bytes consequently become a new parameter header and control parser traversal.
* +1 Reliable strong DoS. A decoded zero length prevents loop progress in softirq context and produces a CPU soft lockup.
Paranoid-only signal:
* +1 Active traversal influence. The semantic mismatch directly controls the iterator offset and progress, so the reinterpreted control information affects active kernel traversal rather than passive metadata.
Important non-awarded signals:
* The ERR_CAUSE read crosses the logical parameter boundary but remains within the received skb. No kernel-memory disclosure is established.
* No write, UAF, controlled reclaim, callback influence, privilege escalation, or arbitrary read/write is demonstrated.
* No extra Availability point was awarded because it would duplicate the same soft-lockup consequence.
* No common-networking-path bonus was awarded because SCTP ADD-IP is narrower than ordinary TCP/IP receive processing.
* No rarity penalty was applied merely because SCTP ADD-IP is optional.
* No privilege or race penalty was applied. Packet construction is deterministic after the required association state exists.
3. Reachability analysis
The attacker is a remote SCTP peer participating in an ADD-IP-enabled association with an outstanding ASCONF request. The crafted response can pass authentication because the predefined empty key identifier allows the peer to derive the association HMAC from exchanged parameters.
No local execution, host capability, or namespace-scoped privilege is needed for the packet trigger. Enabling SCTP ADD-IP and creating the association are deployment prerequisites, but once exposed, the vulnerable operation is directly controlled by peer traffic. No special hardware, timing race, or local control-plane operation is required.
4. Primitive and severity interpretation
The exact primitive is a verifier-consumer parser discrepancy. Input validated as a padded SCTP parameter sequence is later consumed with raw, unpadded offsets, causing attacker-controlled bytes to be reinterpreted as active parameter control information.
This is not a UAF or heap-corruption primitive. The associated OOB read is bounded by the skb and has no demonstrated disclosure path. The established consequence is remote CPU soft lockup and denial of service.
PrimitiveClass is CLASS_A under the strong semantic-reinterpretation rule because the same attacker-controlled representation is validated and consumed under inconsistent semantics that directly govern active traversal. This does not establish code execution or confidentiality and integrity impact.
ImportantCandidate is YES because the remote parser discrepancy is deterministic and crosses validation semantics, although the demonstrated impact remains DoS. AutoDowngradeAllowed is NO because automatically reducing it to an ordinary malformed-packet crash would discard the established semantic reinterpretation and direct remote trigger.
5. One-sentence report phrase
A remote SCTP peer can exploit inconsistent padded and unpadded ASCONF-ACK parameter parsing to force a non-progressing softirq loop and CPU soft lockup, while the related bounded read remains inside the received skb and provides no demonstrated disclosure or write primitive.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The issue is directly network-triggerable and contains a concrete verifier-consumer semantic mismatch, although current evidence supports remote DoS rather than memory corruption or privilege escalation.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: sctp: fix soft lockup from unpadded ASCONF-ACK parameter iteration [ Upstream
Commit: abf59d7f6fff23227256e8199aca5ade45758f8b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=abf59d7f6fff23227256e8199aca5ade45758f8b
Changed files:
net/sctp/sm_make_chunk.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=abf59d7f6fff23227256e8199aca5ade45758f8b
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98123 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98123
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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 7.5
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: 5
Paranoid ActionableScore: 6
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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