[CVE-2026-98449][MODERATE REGULAR] smb: client: delete compound mids on send failure before unlock

[CVE-2026-98449][MODERATE REGULAR] smb: client: delete compound mids on send failure before unlock

[AL-KERNEL]

CVE: CVE-2026-98449
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: smb: client: delete compound mids on send failure before unlock
Commit: 70783946f3b5d0c06ec7df0f5e7bec2bfad24efb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=70783946f3b5d0c06ec7df0f5e7bec2bfad24efb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98449
Analysis date: Mon, 19 Oct 2026 05:23:25 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
An SMB client send failure can race with reconnect processing and return compound request credits twice, corrupting in_flight accounting and triggering a warning with possible SMB request or reconnect disruption.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98449 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98449

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98449	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98449 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-682;CWE-667;Other CVSS 'AV:A/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'A race in the SMB client send error path can leave compound request mids on pending_mid_q while the server lock is released. A concurrent reconnect can process those mids through cifs_abort_connection and return their credits before compound_send_recv returns the same credits again. This can decrement in_flight twice, trigger a WARN in smb2_add_credits, corrupt SMB credit accounting, and potentially stall requests or repeated reconnect processing. For the CVSS the PR:N is selected because a malicious SMB peer does not require an account or privileges on the client after the client has established the relevant connection. The issue is potentially network influenced by an SMB server or network peer able to cause a socket send failure, although reliable triggering depends on a concurrent reconnect and therefore AC:H is appropriate. The demonstrated impact is availability degradation. A host wide crash, information disclosure, privilege escalation, UAF, or arbitrary write is not established. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 0 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	DANGER DISK SIMPLEFIX ERRORPATH SERVERTOCLIENT LINUS SYZBOT  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=1
ActionableScoreLower=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative signals:

* +0 Bookkeeping and active-state inconsistency. Reconnect callbacks and the original send-error path return the same SMB credits and decrement `in_flight` twice.
* +0 WARN-only demonstrated result. The commit establishes a warning in `smb2_add_credits()`, not a kernel panic, UAF, OOB access, disclosure, or authorization bypass.
* +0 Remote reachability not established. A peer can plausibly contribute to socket failure, but the supplied evidence does not prove reliable control of the complete send-failure and reconnect sequence.
* +0 No timing penalty. Concurrency is involved, but the evidence does not establish a narrow or difficult one-shot race.

Paranoid signals:

* +1 Availability impact is technically plausible because corrupted credit and `in_flight` accounting may stall SMB requests or interfere with reconnect processing.
* No additional crash point was awarded because a host-wide crash is not demonstrated.
* No C or I signal was awarded because only internal SMB accounting corruption is established.

Important non-awarded signals:

* No real UAF or repeated object-lifetime release is established. Returning credits twice is not equivalent to dropping an object reference twice.
* `delete_mid()` in the fix prevents pending-list callbacks and duplicate cleanup, but the supplied control flow does not establish that the old behavior freed a mid and then reused or released a dangling mid.
* Controlled reclaim, arbitrary write, OOB write, disclosure, LPE, and security-boundary bypass are not demonstrated.
* V33 active-state trust-boundary candidacy is not established. The modified state is active SMB accounting, but no privileged downstream consumer crossing a guest, namespace, or delegated-interface boundary is identified.
* B5-R is not applicable because there is no retry-accumulated heap OOB write.
* B3-PENDING is not applicable because no shared-backing write exists.
* B4-PENDING is not applicable because no authorization decision changes from DENY to ALLOW.

Repeated-release checks:

* First object-lifetime release capable of freeing a mid: not established.
* Exact dangling reference surviving a first lifetime-ending release: not established.
* Second lifetime or refcount mutation: not established.
* Concrete repeated release or refcount +1: not awarded.
* Paranoid repeated-refcount leverage +1: not awarded.
* REAL UAF FLOOR 5: not applicable.

3. Reachability analysis

The vulnerable sequence requires an SMB compound request send failure followed by reconnect processing while the mids remain on `pending_mid_q`. A malicious SMB server or network disruption may influence socket failure, but the evidence does not prove that a remote peer can reliably force the complete ordering.

An SMB connection or mount must already be initiated. Whether that setup requires host UID 0, a mount helper policy, a delegated service, or another below-host-admin interface is not resolved, so `HostAdminRequired` and `RequiresHostUID0` remain `UNKNOWN`.

No user-namespace or network-namespace capability path is supplied. The complete trigger is therefore not established as namespace scoped. No special hardware is required. Repetition may be possible through reconnect attempts, but reliable attacker control is unresolved.

4. Primitive and severity interpretation

The exact primitive is duplicate mutation of SMB credit accounting. Reconnect callbacks return credits and decrement `in_flight`, after which the compound send-error path performs the corresponding accounting again.

This is active logical state, not stale freed storage. The demonstrated operation does not establish an OOB access, post-lifetime object use, refcount takeover, or repeated release of the same potentially freed object. It is therefore `CLASS_C`, not Class B or Class A.

The demonstrated consequence is a WARN and inconsistent accounting. Request stalls or reconnect disruption are plausible but not demonstrated as host-wide failure. Privilege escalation and confidentiality or integrity compromise are unsupported.

`ImportantCandidate=NO` because no independently useful corruption or boundary primitive is established. `AutoDowngradeAllowed=YES` because the remaining evidence supports an ordinary availability and accounting issue. Manual review is still recommended to confirm whether malformed peer behavior can reliably produce repeated credit corruption or a stronger availability consequence.

5. One-sentence report phrase

An SMB client send failure can race with reconnect processing and return compound request credits twice, corrupting in_flight accounting and triggering a warning with possible SMB request or reconnect disruption.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether a malicious SMB peer can reliably force the send-failure and reconnect ordering and whether repeated accounting corruption causes a persistent SMB stall or host-wide failure.

7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: smb: client: delete compound mids on send failure before unlock
Commit: 70783946f3b5d0c06ec7df0f5e7bec2bfad24efb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=70783946f3b5d0c06ec7df0f5e7bec2bfad24efb

Commit description:

When sending a compound request fails, smb_send_rqst() kicks off a
reconnect. compound_send_recv() still has those mids on pending_mid_q,
but it unlocks the server without removing them first.

During reconnect, cifs_abort_connection() walks pending_mid_q and runs
each mid callback. With no response yet, those callbacks return credits
and drop in_flight. Then compound_send_recv()'s send-error path returns
the same credits again. in_flight ends up decremented twice and
smb2_add_credits() WARNs.

syzbot hits this during SMB2_negotiate when the socket send fails.

cifs_call_async() already calls delete_mid() before unlock on send
failure. Do the same for compound chains and set cancelled_mid[] so the
out: path does not delete them again.

Fixes: ee258d7 ("CIFS: Move credit processing to mid callbacks for SMB3")
Reported-by: syzbot+eeb58d2197d88720a228@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/6a727d22.40259c87.584f4.04ce.GAE@google.com
Tested-by: syzbot+eeb58d2197d88720a228@syzkaller.appspotmail.com
Assisted-by: LLM
Cc: stable@vger.kernel.org
Signed-off-by: Adarsh Das <adarshdas950@gmail.com>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/client/transport.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=70783946f3b5d0c06ec7df0f5e7bec2bfad24efb

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98449 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98449

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:A/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).