* [CVE-2026-97567][MODERATE REGULAR] mptcp: prevent race between disconnect() and rtx [ Upstream
@ 2026-09-25 10:52 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-25 10:52 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97567
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mptcp: prevent race between disconnect() and rtx [ Upstream
Commit: 374da2b9be1280695ce41f108334a8f16e3e54be
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=374da2b9be1280695ce41f108334a8f16e3e54be
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97567
Analysis date: Fri, 25 Sep 2026 06:52:49 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97567 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97567
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-97567 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97567 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race exists between MPTCP disconnect processing and retransmission or timeout timer execution. The disconnect path can close the MPTCP socket while a timer callback is still running or can begin running, resulting in inconsistent socket state and potentially disrupting MPTCP connectivity. For the CVSS the PR:L because a local process must create and control an MPTCP socket and trigger disconnect or close operations. A remote peer may influence retransmission timing but cannot independently invoke the local disconnect path. The issue is not directly network reachable. The patch context does not demonstrate a use after free, out of bounds access, information disclosure, or write primitive. Impact is primarily local denial of service or connection failure. The paranoid availability assessment allows A:H for a timer race in the network stack, but confidentiality and integrity remain N. ';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES REMOTE DANGER SIMPLEFIX RACE ERRORPATH NETWORK TIMER LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 YES NO guess
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap was applied.
2. Signal breakdown
* +1 Local unprivileged trigger. An ordinary local process can create and control its own MPTCP socket and invoke disconnect or close. No host-admin-equivalent capability is established as necessary for the local socket operation.
* +1 Availability impact realistic. The patch establishes an inconsistent MPTCP socket state caused by concurrent disconnect and retransmission or timeout timer activity. This can disrupt the affected MPTCP connection or leave it in an invalid state.
Non-awarded signals:
* +0 Real UAF. No freed object, stale post-free reference, refcount misuse, second release, or lifetime-ending operation is established.
* +0 Memory corruption. The patch does not establish an out of bounds access, invalid memory access, write primitive, type confusion, or controlled corruption.
* +0 Reliable kernel crash. The supplied commit describes inconsistent status, not an Oops, panic, BUG, or demonstrated host-wide crash.
* +0 Remote reachability. A remote peer can influence retransmission timing but cannot independently invoke the local disconnect path. The complete trigger requires a local process controlling the MPTCP socket.
* +0 Strong or weak LPE leverage. No controlled reclaim, callback influence, attacker-controlled post-free state, arbitrary write, disclosure, or security-boundary bypass is shown.
* +0 Race penalty. The issue is a race, but the supplied evidence does not establish a uniquely narrow, one-shot, externally uncontrollable, or difficult-to-repeat timing condition.
* +0 Broad common networking path. MPTCP is a network-stack feature, but the supplied evidence does not establish that this particular disconnect and timer interaction is broadly exposed in default deployments.
3. Reachability analysis
The evaluated attacker is a local process controlling an MPTCP socket. Such a process can invoke close or disconnect operations and can create network activity that causes retransmission or timeout timer handling.
No host-admin-equivalent privilege is shown to be required for creating and closing an ordinary MPTCP socket. Therefore HostAdminRequired is NO. The exact availability and enablement of MPTCP depend on kernel configuration and deployment policy, but this is not evidence that host administration is required for the vulnerable operation.
NamespaceScopedPrivilege is UNKNOWN. The trigger does not appear to require a capability evaluated in a user or network namespace. A network namespace may be usable for testing, but namespace use is not required to establish the local trigger.
A remote peer can contribute to retransmission conditions, but it cannot independently call the local disconnect path. This is not a directly network-triggerable vulnerability under the stated rules.
No special hardware, device assignment, boot option, privileged control-plane setup, or prior host-admin provisioning is established by the supplied patch.
Race repeatability is unresolved. A local process can repeatedly create and close connections, but the patch does not demonstrate that the relevant timer and disconnect interleaving is reliably attacker-controlled.
4. Primitive and severity interpretation
The exact primitive is a timer synchronization and socket-state race. `mptcp_disconnect()` changes the socket state to `TCP_CLOSE` while MPTCP retransmission or timeout timer callbacks may still be executing or may begin execution when asynchronous timer cancellation is used.
The fix replaces asynchronous timer stopping with `sk_stop_timer_sync()`, which waits for an active callback to complete before disconnect processing continues. This establishes that concurrent timer activity could observe or modify socket-related state after disconnect begins.
This is not a real UAF. The supplied patch does not show that `struct mptcp_sock`, `struct sock`, or `struct inet_connection_sock` is freed before a timer callback dereferences it. It also does not show a second release, refcount mutation, stale object reuse, or post-free structured-object processing.
The affected objects are active networking state, but the demonstrated stale condition is limited to inconsistent protocol or timer state. There is no evidence of attacker-controlled replacement, callback dispatch from corrupted memory, pointer manipulation, object substitution, information disclosure, integrity impact, or privilege escalation.
PrimitiveClass is CLASS_C because the demonstrated behavior is invalid-state and availability-oriented behavior without an independently useful corruption primitive.
ImportantCandidate is NO because there is no Class A primitive and no meaningful Class B lifetime or corruption primitive requiring Important-versus-Moderate exploitation review.
AutoDowngradeAllowed is YES because the patch-supported consequence is connection-level denial of service or inconsistent MPTCP behavior. No unresolved memory-corruption, authorization, ownership, or security-boundary primitive is established.
Likely operational severity is ordinary Moderate or Low-like. Systems actively using MPTCP may experience affected connection disruption. The supplied evidence does not support host compromise, local privilege escalation, confidentiality impact, integrity impact, or a host-wide kernel crash.
5. One-sentence report phrase
A race between MPTCP disconnect processing and retransmission or timeout timer execution can leave an MPTCP socket in an inconsistent state and disrupt the affected connection, with a local process controlling the socket required for triggering.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
The patch fixes timer synchronization in a network protocol state transition, but the supplied context establishes only inconsistent socket state and connection disruption rather than a concrete UAF, kernel crash, or memory-corruption primitive.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: mptcp: prevent race between disconnect() and rtx [ Upstream
Commit: 374da2b9be1280695ce41f108334a8f16e3e54be
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=374da2b9be1280695ce41f108334a8f16e3e54be
Changed files:
net/mptcp/protocol.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=374da2b9be1280695ce41f108334a8f16e3e54be
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97567 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97567
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:L/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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