* [CVE-2026-97566][LOW] mptcp: pm: kernel: drop pending ADD_ADDR when removing ID0
@ 2026-09-25 16:16 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-25 16:16 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97566
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mptcp: pm: kernel: drop pending ADD_ADDR when removing ID0
Commit: d4a67a880654e1bfe318a31bea0bdbb026a09ade
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d4a67a880654e1bfe318a31bea0bdbb026a09ade
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97566
Analysis date: Fri, 25 Sep 2026 12:16:04 -0400
ActionableScore: 1
ActionableScore lower bound: 0
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-2026-97566 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97566
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: LOW
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-2026-97566 LOW https://www.kernelcve.org/list/?q=CVE-2026-97566 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-664;*CWE-672;CWE-703;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A stale pending ADD_ADDR announcement can remain in the in kernel MPTCP path manager after removal of the ID0 endpoint. If ID0 is later selected again after a signal endpoint update, the stale anno_list entry can trigger WARN_ON_ONCE in mptcp_pm_announced_alloc and disrupt MPTCP path manager operation. For the CVSS the PR:L paranoid score assumes an attacker has delegated network administration capabilities such as CAP_NET_ADMIN in a service or container context. The issue is not directly network reachable because triggering requires local MPTCP endpoint control plane operations rather than network packet input. Impact is normally limited to a warning and local denial of service. A system configured to panic on warnings can experience a kernel crash. No memory corruption primitive or privilege escalation path is demonstrated by the patch.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES REMOTE DANGER NETWORK LINUS SYZBOT DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
ActionableScoreLower=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap was applied. The paranoid point reflects the conditional availability consequence where a deployment converts WARN_ON into a fatal kernel event through panic_on_warn or an equivalent warning escalation policy.
2. Signal breakdown
* Conservative score: 0 points. The patch establishes a stale logical MPTCP path-manager announcement entry and a WARN_ON_ONCE condition, but does not establish memory corruption, lifetime violation, authorization bypass, information disclosure, integrity impact, or a reliable kernel crash.
* Paranoid availability signal: +1. A stale anno_list entry can reach WARN_ON_ONCE in mptcp_pm_announced_alloc. If warning escalation is enabled, this can result in a kernel panic and local denial of service.
* Remote reachability: not awarded. The vulnerable operation is reached through MPTCP endpoint control-plane operations, not directly through received MPTCP packets.
* Local unprivileged trigger: not awarded. The complete endpoint creation, signal endpoint update, ID0 removal, and re-selection sequence is not established as reachable by an ordinary unprivileged user.
* Controlled reclaim, arbitrary write, invalid memory access, and post-free object reuse: not demonstrated.
* Structured stale-object leverage: not awarded. anno_list is stale path-manager bookkeeping, and the demonstrated use is a consistency warning rather than active consumption of attacker-controlled reclaimed object fields.
* Confidentiality and integrity: not awarded. No disclosure path or unauthorized modification is established.
* Reliable kernel crash: not awarded in the conservative score. WARN_ON_ONCE alone is not a demonstrated fatal condition.
* Concrete persistent reference or resource leak: not awarded. The patch removes a stale announcement entry, but supplied evidence does not establish unbounded or unrecoverable resource accumulation.
3. Reachability analysis
The trigger requires MPTCP kernel path-manager control-plane operations that remove the ID0 endpoint and later add or select another signal endpoint. These operations are performed through MPTCP netlink endpoint management rather than ordinary packet processing.
CAP_NET_ADMIN or equivalent network-management authority is likely relevant to endpoint management, but the supplied patch does not show the netlink policy checks or establish whether every required operation is permitted in an attacker-controlled network namespace. Therefore HostAdminRequired and NamespaceScopedPrivilege are both UNKNOWN.
No special hardware is involved. No race or narrow timing window is demonstrated. The sequence is a deterministic stale-state condition after a specific endpoint-management order, but attacker reachability to the complete privileged control-plane sequence is unresolved.
4. Primitive and severity interpretation
The exact defect is stale logical state. Removing ID0 fails to remove a matching pending ADD_ADDR entry from anno_list and fails to adjust add_addr_signaled. A later path-manager operation finds the stale entry and reaches WARN_ON_ONCE.
This is not a UAF. The patch does not show an object being freed while a stale reference is dereferenced, nor does it show a second release, refcount mutation, out-of-bounds access, list corruption, arbitrary write, or stale-object reuse. The applicable classification is PrimitiveClass=NONE.
The demonstrated consequence is an MPTCP path-manager consistency failure and WARN_ON_ONCE. The speculative stronger consequence is a kernel panic only on systems configured to make warnings fatal. No privilege-escalation, confidentiality, integrity, or security-boundary-bypass mechanism is supported by the patch.
ImportantCandidate is NO because no Class A or Class B primitive is present. AutoDowngradeAllowed is YES because the issue is a constrained stale bookkeeping condition with no unresolved memory-corruption or authorization primitive.
5. One-sentence report phrase
A stale MPTCP ADD_ADDR announcement can survive ID0 endpoint removal and later trigger WARN_ON_ONCE when the kernel path manager reselects the endpoint, causing at most a local denial of service on systems configured to panic on warnings.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch establishes a stale MPTCP bookkeeping entry and warning path only. No memory corruption, UAF, authorization bypass, direct network trigger, or plausible privilege-escalation primitive is demonstrated.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: mptcp: pm: kernel: drop pending ADD_ADDR when removing ID0
Commit: d4a67a880654e1bfe318a31bea0bdbb026a09ade
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d4a67a880654e1bfe318a31bea0bdbb026a09ade
Commit description:
The in-kernel MPTCP path manager can leave a stale ADD_ADDR announcement
entry alive when removing the id 0 endpoint. This happens because the id 0
removal path does not tear down pending announcements, unlike the non-zero
id path.
When the PM later reselects id 0 after adding another signal endpoint, it
finds the stale anno_list entry and hits WARN_ON_ONCE(mptcp_pm_is_kernel())
in mptcp_pm_announced_alloc().
Root cause: asymmetry between removal paths.
- Non-zero id path: mptcp_nl_remove_subflow_and_signal_addr() calls
mptcp_pm_remove_announced() to clean up.
- Id 0 path: mptcp_nl_remove_id_zero_address() skips cleanup entirely.
Fix by making the id 0 path symmetric: call mptcp_pm_announced_remove()
and decrement add_addr_signaled before queuing the RM_ADDR.
Subtle detail: signal endpoints are stored in anno_list with port 0, but
msk_local carries the connection's local port. In other words, entries
linked to ID0 paths should have port == 0. A follow-up patch will ensure
that. mptcp_pm_announced_remove() uses use_port=true for comparison. So
clear the port before the lookup.
Fixes: 740d798 ("mptcp: remove id 0 address")
Cc: [email protected]
Reported-by: [email protected]
Closes : multipath-tcp/mptcp_net-next#620
Suggested-by: Tao Cui <[email protected]>
Signed-off-by: Kalpan Jani <[email protected]>
Reviewed-by: Matthieu Baerts (NGI0) <[email protected]>
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
Link: https://patch.msgid.link/20260908-net-mptcp-misc-fixes-7-3-rc1-v2-4-df1de70348b6@kernel.org
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/mptcp/pm_kernel.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=d4a67a880654e1bfe318a31bea0bdbb026a09ade
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97566 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97566
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:L
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: 0
Paranoid ActionableScore: 1
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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