* [CVE-2026-97522][LOW] mptcp: fix bad accounting in __mptcp_subflow_push_pending()
@ 2026-09-25 13:00 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-25 13:00 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97522
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mptcp: fix bad accounting in __mptcp_subflow_push_pending()
Commit: 9781fa35d9f7a87a83115acd3a88bc9ce35b5407
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9781fa35d9f7a87a83115acd3a88bc9ce35b5407
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97522
Analysis date: Fri, 25 Sep 2026 09:00:38 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
An MPTCP accounting error added failed subflow push return values to the copied byte counter, causing inconsistent later send accounting without a demonstrated security impact.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97522 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97522
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-2026-97522 LOW https://www.kernelcve.org/list/?q=CVE-2026-97522 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:N';CWE-682;CWE-703;BEST CVSS score: '0';DESCR 'An MPTCP byte accounting error occurs when __subflow_push_pending returns an error and its nonpositive return value is still added to the copied counter. This can leave internal send accounting inconsistent for a later push operation, but the patch context does not show a memory safety primitive, information disclosure, privilege escalation, kernel crash, or reliable denial of service. The issue is a correctness problem in local MPTCP socket processing and is not directly network reachable. No confidentiality integrity or availability impact is supported by the available code change.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES REMOTE SIMPLEFIX NETWORK DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=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: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap was applied.
## 2. Signal breakdown
* +0 Passive accounting inconsistency. A nonpositive error return from `__subflow_push_pending()` was added to `copied`, causing later MPTCP push accounting to become inconsistent.
* +0 Memory corruption. No UAF, double free, stale reference, refcount misuse, OOB access, invalid pointer use, or write primitive is established.
* +0 Availability impact. The supplied patch and commit message do not demonstrate a kernel crash, socket hang, resource exhaustion, or reliable DoS.
* +0 Confidentiality and integrity impact. No disclosure, unauthorized modification, policy bypass, or privilege escalation mechanism is shown.
* +0 Remote reachability. The affected code belongs to networking, but the defect is reached through local socket processing and no remote attacker-controlled trigger to a security consequence is established.
* +0 Local unprivileged trigger. A complete trigger path and its privilege requirements are not visible. This does not affect the score because no security-relevant primitive is established.
Important non-awarded signals:
* Controlled reclaim is not demonstrated.
* Arbitrary or directed write is not demonstrated.
* A concrete repeated release or refcount operation is not present.
* No crash-related Availability point is awarded.
* No C or I impact is awarded merely because incorrect byte accounting might theoretically affect later MPTCP behavior.
* No paranoid uplift is justified. The patch establishes an accounting correction only.
## 3. Reachability analysis
The affected function processes MPTCP send-side state for a socket and calls `__subflow_push_pending()`. On an error return, the pre-fix code added a nonpositive value to the local `copied` counter even though no bytes were successfully pushed.
The supplied context does not show the complete socket creation, MPTCP enablement, error-generation, or later use of the incorrect accounting value. Therefore, whether an ordinary local user can reliably trigger the full condition is unresolved. `HostAdminRequired=UNKNOWN` is used because the evidence does not establish either a host-admin requirement or a complete below-host-admin security-relevant trigger.
No namespace-specific capability operation is shown. `NamespaceScopedPrivilege=UNKNOWN` is appropriate. No prior host setup, special hardware, sysctl dependency, race condition, or remote packet-triggered security consequence is established by the patch.
## 4. Primitive and severity interpretation
The exact defect is a bookkeeping error:
`__subflow_push_pending()` returns an error or zero
-> `copied += ret` still executes
-> later push processing may observe inconsistent byte accounting.
This is not an active structured-object lifetime violation. It is not fixed stale storage, because no stale storage exists. It is not a cleanup/destructor issue. There is no first lifetime operation that may free an object, no surviving dangling reference, and no second lifetime or refcount mutation.
The appropriate classification is `PrimitiveClass=NONE`. The demonstrated consequence is incorrect internal send accounting after an error. A kernel crash, memory corruption, information disclosure, integrity impact, local privilege escalation, and network-triggerable DoS are speculative and unsupported by the supplied patch.
`ImportantCandidate=NO` because there is no meaningful corruption, authorization, ownership, lifetime, or boundary-bypass primitive requiring Important-versus-Moderate review. `AutoDowngradeAllowed=YES` because automatic closure would not discard an unresolved concrete security primitive.
Likely operational severity is a non-security correctness issue. It may affect MPTCP send behavior after an error, but the available evidence does not support CVE-level confidentiality, integrity, or availability impact.
## 5. One-sentence report phrase
An MPTCP accounting error added failed subflow push return values to the copied byte counter, causing inconsistent later send accounting without a demonstrated security impact.
## 6. Manual review recommendation
NO MANUAL CHECK NEEDED
The available patch establishes only a local accounting correction and does not show a memory-safety, authorization, disclosure, privilege-escalation, crash, or reliable denial-of-service primitive.
## 7. Call-site confidence
Call-site confidence: low
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: mptcp: fix bad accounting in __mptcp_subflow_push_pending()
Commit: 9781fa35d9f7a87a83115acd3a88bc9ce35b5407
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9781fa35d9f7a87a83115acd3a88bc9ce35b5407
Commit description:
If __subflow_push_pending() errors out we should avoid updating the
copied byte counters, to avoid mismatch push call later on.
Fixes: 0fa1b37 ("mptcp: use get_send wrapper")
Cc: [email protected]
Signed-off-by: Paolo Abeni <[email protected]>
Reviewed-by: Matthieu Baerts (NGI0) <[email protected]>
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
Link: https://patch.msgid.link/20260917-net-mptcp-misc-fixes-7-3-rc4-v2-3-0cf5c72667c8@kernel.org
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
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=9781fa35d9f7a87a83115acd3a88bc9ce35b5407
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97522 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97522
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: Not available
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:N
The Best / paranoid CVSS score: 0
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: 0
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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