* [CVE-2026-98130][MODERATE 7.0] sctp: fix a TOCTOU race in SCTP_CMD_TIMER_START [ Upstream
@ 2026-09-28 14:10 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-28 14:10 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98130
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: sctp: fix a TOCTOU race in SCTP_CMD_TIMER_START [ Upstream
Commit: e42ba56281ca3ae2dcb3558bebee9a1c9a4831d9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e42ba56281ca3ae2dcb3558bebee9a1c9a4831d9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98130
Analysis date: Mon, 28 Sep 2026 10:10:36 -0400
ActionableScore: 5
ActionableScore lower bound: 4
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-2026-98130 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98130
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-2026-98130 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98130 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-367;CWE-362;*CWE-416;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'A TOCTOU race in the SCTP_CMD_TIMER_START handler can occur because timer_pending and timer_reduce previously examined and changed the timer state in separate operations. The timer may expire and detach between these operations, after which timer_reduce can arm it again without acquiring the association reference required by the new timer instance. The later timer callback unconditionally drops an association reference, which can unbalance the reference count and cause a use after free of the SCTP association during teardown. A remote SCTP peer may be able to drive the protocol state machine into the affected timer path, but successful triggering depends on winning a narrow timer expiration race. For the CVSS the PR:N value is used because no authenticated or privileged access is required when an attacker can exchange SCTP traffic with the affected endpoint. AC:H reflects the timing dependent race. Impact is at least remote denial of service through a kernel crash and in the worst case may include confidentiality and integrity impact if reuse of the freed association can be influenced. Systems are exposed only when SCTP support is enabled and an affected SCTP endpoint is reachable.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE RACE UAF NETWORK TIMER LINUS KPANIC DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Applied conservative floor: 2 -> 4 under REAL UAF FLOOR 4.
* No paranoid floor or cap was applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2 Real UAF / lifetime violation. A timer is rearmed without acquiring its required association reference. Its callback later drops an unowned reference, allowing premature association destruction followed by use during teardown.
* +1 Reliable kernel crash / strong DoS. A freed SCTP association used during teardown can realistically cause an Oops or kernel crash.
* -1 Hard timing window. The timer must expire and detach specifically between `timer_pending()` and `timer_reduce()`, and direct control over this interleaving is not established.
* Raw conservative total: 2.
* REAL UAF FLOOR 4 applies because a stale association is actually used, host-admin privilege is not positively established, and this is not a fixed stale buffer with an immediate shallow fault.
Additional paranoid signals:
* +2 Remote reachability. A reachable SCTP peer can plausibly drive the SCTP state machine and affected timer path through network traffic. The exact packet-to-command call path is not supplied, so this is retained in the paranoid score rather than the conservative score.
* +1 Attacker-influenced lifetime manipulation. A peer can plausibly create associations and repeatedly drive protocol events affecting timer state and association teardown. This is technically defensible but not fully established by the shown call sites.
* Paranoid arithmetic: +2 UAF, +1 crash, +2 remote reachability, +1 lifetime influence, -1 timing = 5.
Not awarded:
* Concrete repeated release/refcount +1 was not awarded. The old timer callback drops its valid timer reference, while the later callback drops a reference that was never acquired and may prematurely destroy the association. The evidence does not show a first put freeing the object followed by a second put through that already dangling reference.
* Paranoid repeated-refcount leverage +1 was withheld for the same reason.
* FLOOR 5 was not applied through the repeated-release exception.
* Structured stale-object leverage was not awarded. The exact post-free teardown operation and fields consumed are not visible.
* Weak LPE and strong exploitation leverage were not awarded. Controlled reclaim, attacker-shaped replacement contents, callback control, arbitrary read/write, and refcount takeover are not demonstrated.
* Confidentiality and integrity points were not awarded merely because the UAF could theoretically affect reclaimed memory.
* No extra Availability point was awarded because the likely kernel crash is already counted.
* Common networking-core exposure was not awarded because SCTP is not equivalent to a broadly exercised TCP/IP fast path.
3. Reachability analysis
The likely attacker is a remote SCTP peer communicating with an already reachable SCTP endpoint. Such a peer can influence association state and protocol events without local credentials, but the supplied diff does not show which network event emits the affected `SCTP_CMD_TIMER_START` or whether every required transition is remotely controllable.
Consequently, below-host-admin reachability is plausible but not conclusively established for the complete trigger, so `HostAdminRequired=UNKNOWN`. No local capability check or namespace setup is shown. The complete operation is therefore not proven namespace-scoped, resulting in `NamespaceScopedPrivilege=UNKNOWN`.
An SCTP endpoint must already be configured and reachable, but no unusual hardware, boot mode, or device prerequisite exists. The race window is narrow because expiration and detachment must occur between two adjacent timer operations. Repeated association and protocol activity may provide multiple attempts, but reliability is unresolved.
4. Primitive and severity interpretation
The exact primitive is an association lifetime imbalance. `timer_reduce()` may arm a new timer without the corresponding `sctp_association_hold()`. The later callback unconditionally releases an association reference, potentially destroying the active `struct sctp_association` too early. Teardown can then operate on the freed association.
This is an active structured-object lifetime violation and a real UAF, not merely a NULL dereference, warning, or passive accounting error. It is classified as CLASS_B because premature destruction and stale use are concrete, but controlled reclamation or another independently useful post-free primitive is not established.
This differs from a concrete repeated-release UAF. The vulnerable callback performs an unmatched put that can cause premature destruction, but the supplied evidence does not establish that it mutates refcount storage after the object has already been freed. The demonstrated practical consequence is kernel crash or DoS. Privilege escalation, information disclosure, and arbitrary kernel modification remain speculative.
`ImportantCandidate=YES` because a potentially network-reachable active-object UAF leaves meaningful exploitation questions unresolved. `AutoDowngradeAllowed=NO` because automatic closure would discard that unresolved lifetime-corruption surface, even though the available evidence does not independently justify CLASS_A or a score of 7 or higher.
5. One-sentence report phrase
A timing race can rearm an SCTP association timer without taking its required reference, allowing a later callback to prematurely release the association and cause a potentially remote use-after-free and kernel crash during teardown.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Confirm the remotely reachable SCTP event sequence, affected timer types, association allocator and teardown behavior, race repeatability, and whether reclaimed association memory can be influenced before the stale teardown operation.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: sctp: fix a TOCTOU race in SCTP_CMD_TIMER_START [ Upstream
Commit: e42ba56281ca3ae2dcb3558bebee9a1c9a4831d9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e42ba56281ca3ae2dcb3558bebee9a1c9a4831d9
Changed files:
net/sctp/sm_sideeffect.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=e42ba56281ca3ae2dcb3558bebee9a1c9a4831d9
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98130 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98130
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:L/I:L/A:H
The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 8.1
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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