* [CVE-2026-98167][MODERATE 7.0] smb: client: fix server->total_read for compound encrypted PDUs
@ 2026-10-06 18:20 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-06 18:20 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98167
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: smb: client: fix server->total_read for compound encrypted PDUs
Commit: 8703539d22fdbc13dd2db090ee199c3a427b8ea0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8703539d22fdbc13dd2db090ee199c3a427b8ea0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98167
Analysis date: Tue, 06 Oct 2026 14:20:49 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98167 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98167
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98167 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98167 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H';CWE-125;CWE-130;*CWE-20;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.2';DESCR 'The SMB client can validate an encrypted compound response against the size of the complete decrypted frame instead of the size of the current sub-PDU. A malicious or compromised SMB server can send a truncated non-last sub-PDU with a crafted NextCommand value so that smb2_check_message accepts it and smb2_get_data_area_len performs an out-of-bounds read. For the CVSS the PR:N value is used because the attacker needs no privileges on the affected client and only needs control of an SMB server used by that client. The issue is network reachable after an SMB session has been established and can cause a client kernel crash or denial of service. The paranoid score also considers limited confidentiality impact from the out-of-bounds read. There is no demonstrated write primitive, so integrity impact and privilege escalation are not included in the score. SMB services are commonly limited to internal or enterprise networks, but a compromised trusted file server can still expose many connected clients.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) MAYBE OOB DISK SIMPLEFIX SERVERTOCLIENT LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 4.
* Conservative score: 4.
* Raw paranoid score: 5.
* Paranoid score: 5.
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate**::
2. Signal breakdown
Conservative signals:
* +2 Remote network reachability. A malicious or compromised SMB server can return the malformed encrypted compound response directly to an established client.
* +1 Weak or indirect corruption candidate. Attacker-controlled sub-PDU boundaries cause an internal out-of-bounds read and structured length misinterpretation, but no write or disclosure primitive is established.
* +1 Reliable kernel crash or strong DoS. An unchecked kernel OOB read can fault while the SMB client processes the response.
* Total: 2 + 1 + 1 = 4.
Paranoid additional signal:
* +1 Broadly deployed exposure. SMB clients are common, and encrypted compound responses are realistic in enterprise deployments, although an active encrypted SMB session is required.
* Total: 4 + 1 = 5.
Not awarded:
* No confidentiality point. The kernel reads beyond the current sub-PDU, but no path returning those bytes to the server or userspace is shown.
* No integrity point. No OOB write, UAF, arbitrary write, or persistent state corruption is established.
* No strong semantic-reinterpretation score. Although adjacent PDU bytes can be interpreted under the wrong command boundary, the supplied evidence establishes only an OOB read and possible crash, not a security-useful active operation.
* No extra availability point. It would duplicate the same kernel crash.
* No LPE or controlled-reclaim points.
* No UAF, repeated release, refcount mutation, or lifetime floor applies.
3. Reachability analysis
The evaluated attacker controls or compromises an SMB server to which the victim SMB client has an established encrypted session. The attacker needs no local account, capability, or host-administrator privilege on the client, so HostAdminRequired is NO.
An SMB mount and negotiated encrypted connection must already exist. This is prior deployment setup, but the remote attacker does not need to perform a privileged operation on the victim when delivering the malformed response. Namespace-scoped privileges are not relevant to the demonstrated remote-server path and remain UNKNOWN.
No special hardware, boot option, race, or narrow timing window is required. Triggering depends on SMB client use, encryption, compound response processing, and attacker control over the connected server.
4. Primitive and severity interpretation
The exact primitive is an attacker-induced out-of-bounds kernel read caused by validating a truncated non-last sub-PDU against the length of the complete decrypted compound frame. It is neither a UAF nor an ownership or lifetime violation.
The demonstrated behavior is a malformed-message validation bypass with potential kernel crash. No disclosure channel, subsequent write, callback influence, controlled object corruption, or privilege escalation is established. It is therefore CLASS_C rather than CLASS_A or CLASS_B.
ImportantCandidate is NO because the evidence does not establish an independently useful corruption or security-boundary primitive. AutoDowngradeAllowed is YES because the known impact remains a network-triggerable OOB-read and DoS issue, although its network exposure warrants manual confirmation rather than immediate closure.
5. One-sentence report phrase
A malicious or compromised SMB server can send a truncated encrypted compound sub-PDU that bypasses per-PDU length validation and causes an out-of-bounds read in the client kernel, potentially resulting in denial of service.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Review the complete consumers of values returned by smb2_get_data_area_len to confirm that attacker-influenced offsets cannot cause a later write, disclosure, or stronger semantic reinterpretation.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: smb: client: fix server->total_read for compound encrypted PDUs
Commit: 8703539d22fdbc13dd2db090ee199c3a427b8ea0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8703539d22fdbc13dd2db090ee199c3a427b8ea0
Commit description:
In receive_encrypted_standard(), server->total_read is left at the
full decrypted frame size when walking sub-PDUs of a compound encrypted
frame. As a result, cifs_handle_standard() passes this full size
to smb2_check_message(), causing the PDU length guards to incorrectly
validate the entire compound frame instead of the current sub-PDU.
This allows truncated non-last sub-PDUs to bypass length validation,
leading to out-of-bounds reads in smb2_get_data_area_len().
Fix this by setting server->total_read to the true length of the
current sub-PDU: next_cmd for non-last sub-PDUs, and the remaining
pdu_length for the last one.
Fixes: b24df3e ("cifs: update receive_encrypted_standard to handle compounded responses")
Cc: [email protected]
Signed-off-by: Frank Sorenson <[email protected]>
Reviewed-by: David Howells <[email protected]>
Signed-off-by: Paulo Alcantara <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/smb/client/smb2ops.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=8703539d22fdbc13dd2db090ee199c3a427b8ea0
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98167 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98167
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:L/PR:N/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
The Best / paranoid CVSS score: 8.2
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).
^ permalink raw reply [relevance 21%]
Results 1-1 of 1 | reverse | sort options + mbox downloads above
-- links below jump to the message on this page --
2026-10-06 18:20 21% [CVE-2026-98167][MODERATE 7.0] smb: client: fix server->total_read for compound encrypted PDUs AL-KERNEL
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox