* [CVE-2026-99113][MODERATE REGULAR] ksmbd: zero the FS_OBJECT_ID_INFORMATION buffer before filling it in
@ 2026-10-30 16:39 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-30 16:39 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99113
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ksmbd: zero the FS_OBJECT_ID_INFORMATION buffer before filling it in
Commit: 898cb4f2e12a5ddea1b2d821cc642c3100f46da7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=898cb4f2e12a5ddea1b2d821cc642c3100f46da7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99113
Analysis date: Fri, 30 Oct 2026 12:39:37 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A remote authenticated ksmbd client can use a crafted compound request to receive up to 31 bytes of stale data from a preceding failed response.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99113 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99113
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: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-99113 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99113 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE AEGIS_AS=3 LEGACY=MODERATE RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';*CWE-200;CWE-226;CWE-908;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.3';DESCR 'ksmbd can return a 64 byte FS_OBJECT_ID_INFORMATION structure without initializing all bytes. In a crafted SMB compound request, a preceding command can write response data and then fail, after which its short error response allows the following filesystem information reply to overlap stale bytes. A remote authenticated SMB client may therefore receive up to 31 bytes from a response it was not authorized to see, including data associated with an access denied operation. For the CVSS the PR:L value is selected because reliable triggering requires an SMB session able to submit the compound request. The demonstrated primitive is a bounded response buffer information disclosure with C:L and no supported integrity or availability impact. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.3 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE because the ActionableScore threshold rule was applied and the CVSS score, vector or bug class 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 INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 and DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS. The independent weaker Aegis shadow evaluated CVSS 4.3 and ActionableScore 3 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE REMOTE DISK LEAK SKIP LINUS INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=CONFIRMED
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 4.
* Conservative score: 4; no floor or cap applied.
* Raw paranoid score: 4.
* Paranoid score: 4; no additional technically supported effect.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +2 Remote network reachability: an authenticated SMB client can submit the crafted compound request.
* +1 Confidentiality impact: up to 31 stale bytes from an earlier response can be returned.
* +1 Practical exploit chain: preceding response writes data, fails and is shortened, then overlapping `FS_OBJECT_ID_INFORMATION` leaves prior bytes in the transmitted reply.
* No authorization-bypass points: the access-denied decision remains intact; the flaw discloses residual response bytes rather than changing DENY to ALLOW.
* No memory-corruption, UAF, arbitrary-read, integrity, availability, or LPE points. The readout is bounded to stale contents of the allocated compound response buffer.
* No extra broad-exposure point: ksmbd must be enabled and serving an authenticated session.
3. Reachability analysis
A remote authenticated SMB user can invoke the compound-request path; host UID 0, host administrative capabilities, or namespace capabilities are not required. Server deployment and an SMB account/session are prerequisites, but they are not host-admin privileges. The attacker controls request sequencing, while the exact stale bytes depend on the preceding failed response.
4. Primitive and severity reading
The primitive is a bounded cross-response information disclosure caused by partially initializing a 64-byte structure after compound-response overlap. The patch’s `memset()` prevents transmission of stale bytes. Protected response data is demonstrably exposed, including bytes associated with an access-denied operation, but no specific credential, key, or high-value object is identified. This is constrained CLASS_B disclosure, not B4 authorization-state bypass. Important severity is unsupported; automatic Moderate handling remains possible after review.
5. One-sentence report phrase
A remote authenticated ksmbd client can use a crafted compound request to receive up to 31 bytes of stale data from a preceding failed response.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm the sensitivity and repeatability of preceding-response contents; no stronger primitive is shown.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ksmbd: zero the FS_OBJECT_ID_INFORMATION buffer before filling it in
Commit: 898cb4f2e12a5ddea1b2d821cc642c3100f46da7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=898cb4f2e12a5ddea1b2d821cc642c3100f46da7
Commit description:
smb2_get_info_filesystem() reports 64 bytes for FS_OBJECT_ID_INFORMATION,
that is the whole of struct object_id_info, but writes only 46 of them:
- objid[] is 16 bytes, and when the volume UUID is not available only
sizeof(stfs.f_fsid) (8) bytes are copied into it;
- extended_info.version_string[] is STRING_LENGTH (28) bytes, and only
strlen("1.1.0") (5) bytes are copied into it.
The response buffer is zeroed on allocation (kvzalloc() in
smb2_allocate_rsp_buf()), so for a standalone request the remaining 31
bytes are zero. In a compound request they need not be. The offset of
the next response is advanced by the length pinned for the previous one,
so if a preceding command wrote its reply into the buffer and then
failed, smb2_set_err_rsp() pins only the short error response and the
next reply lands inside the area that has already been written. Only
the header is cleared there:
memset((char *)rsp_hdr, 0, sizeof(struct smb2_hdr) + 2);
The client then receives up to 31 bytes of a response it was not meant
to see, including one that failed with an access denied error.
Clear the structure before filling it in. As a side effect
version_string is now NUL terminated.
Fixes: e2f3448 ("cifsd: add server-side procedures for SMB3")
Suggested-by: ChenXiaoSong <[email protected]>
Cc: [email protected]
Signed-off-by: Aleksandr Khromov <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/smb/server/smb2pdu.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=898cb4f2e12a5ddea1b2d821cc642c3100f46da7
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99113 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99113
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:H/PR:L/UI:N/S:U/C:L/I:N/A:N
The Best / paranoid CVSS vector: AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
The Best / paranoid CVSS score: 4.3
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: unknown
Paranoid ActionableScore: 4
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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