From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99272][MODERATE 7.0] smb: client: validate the data area in SMB2_read() Date: Sat, 07 Nov 2026 22:30:15 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99272 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 1ba1937de005e261a8858f45bfef5da7458df94c List-Id: CVE: CVE-2026-99272 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: smb: client: validate the data area in SMB2_read() Commit: 1ba1937de005e261a8858f45bfef5da7458df94c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1ba1937de005e261a8858f45bfef5da7458df94c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99272 Analysis date: Sat, 07 Nov 2026 22:30:15 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: A malicious SMB server can make the client copy up to about 16 KiB beyond a received SMB2 READ response, potentially crashing the kernel and possibly exposing adjacent slab data through a downstream parser. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99272 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99272 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-99272 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99272 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H';CWE-125;*CWE-20;Other CVSS 'AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H';BEST CVSS score: '9.1';DESCR 'SMB2_read trusted the server supplied DataOffset and DataLength without verifying that the complete data area was present in the received response. A malicious SMB server can return a short READ response with DataOffset zero and an oversized DataLength, causing the client to copy beyond the receive object by up to about 16 KiB. The concrete primitive is a kernel slab out of bounds read rather than an out of bounds write or UAF. Availability impact can include a kernel fault or KASAN failure, while limited confidentiality impact is plausible if adjacent kernel data copied into the read buffer becomes observable through symlink parsing or another consumer. For the CVSS the PR:N value is selected because the attacker only needs control of the SMB server response and does not need an account or privileges on the affected client. The base UI:R reflects that the client must access the malicious share or symlink, while the paranoid vector uses UI:N for automated mounts or workloads that perform the affected read without a new human action. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 9.1 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 IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because FD false positive review allowed a downgrade. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS8.5PLUS and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH. The independent weaker Aegis shadow evaluated CVSS 4.3 and ActionableScore 4 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE KASAN OOB DISK LEAK SERVERTOCLIENT LINUS KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS8.5PLUS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 3. * Conservative score: 3; no floor or cap applied. * Raw paranoid score: 4. * Paranoid score: 4; no floor or cap applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown * +1 confirmed slab out-of-bounds read: attacker-supplied `DataOffset` and `DataLength` make `memcpy()` read beyond the received response object. * +1 plausible kernel crash/strong DoS: reads may extend up to roughly 16 KiB beyond the receive object and can fault; KASAN already detects the condition. * +1 broad SMB client exposure: the vulnerable synchronous SMB2 read path is practically exercised by mfsymlink/SFU parsing and is not merely diagnostic code. * Paranoid +1 confidentiality concern: adjacent slab bytes are copied into a caller buffer consumed by a symlink parser. Actual user-visible disclosure is not demonstrated, so this is excluded from the conservative score. * No remote-reachability +2: a malicious server controls the response, but the evidence does not establish that it can induce the required client mount/read without prior client configuration or interaction. * No write, UAF, controlled reclaim, authorization bypass, or integrity impact is shown. * NEW52/B5-R does not apply: this is an OOB read, not a retry-accumulated heap OOB write. * No second availability point is awarded for the same possible fault. 3. Reachability analysis The attacker controls an SMB server response and needs the client to perform the affected synchronous read. The attacker needs no host UID 0, capability, or namespace privilege, but client connection/mount and access to the malicious share remain environmental prerequisites. No race, special hardware, or retry sequence is required. 4. Primitive and severity reading The exact primitive is a bounded-by-request-length slab OOB source read into an adequately sized destination buffer. It is CLASS_C because the supplied evidence establishes invalid reading and possible crash, but not a confirmed disclosure channel or separately useful corruption primitive. A symlink consumer makes disclosure technically plausible, not proven. ImportantCandidate is therefore NO, and automatic Moderate downgrade remains allowed after review. 5. One-sentence report phrase A malicious SMB server can make the client copy up to about 16 KiB beyond a received SMB2 READ response, potentially crashing the kernel and possibly exposing adjacent slab data through a downstream parser. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm whether any affected caller returns or otherwise exposes the copied adjacent slab bytes to userspace. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: smb: client: validate the data area in SMB2_read() Commit: 1ba1937de005e261a8858f45bfef5da7458df94c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1ba1937de005e261a8858f45bfef5da7458df94c Commit description: SMB2_read() copies le32_to_cpu(rsp->DataLength) bytes from (char *)rsp + rsp->DataOffset without checking that the range lies within the response actually received. A READ response with DataOffset == 0 makes smb2_get_data_area_len() zero the data length, so smb2_check_message() accepts a frame as short as the fixed response, while SMB2_read() still uses the server-supplied DataLength, capped only by CIFS_MAX_MSGSIZE and the caller's length. A malicious server can answer the synchronous read used by the mfsymlinks (or SFU) symlink parser with an 81-byte READ response carrying DataOffset 0 and DataLength 1067, making the client copy 1067 bytes from a 448-byte receive object (KASAN slab-out-of-bounds; up to 16 KiB in the general case). Clamp a zero (or header-overlapping) DataOffset to read_rsp_size, as handle_read_data() does for the asynchronous path, and reject the response unless DataOffset + DataLength fits within rsp_iov.iov_len. The SMB1 helper was fixed the same way in 5be5bdd . Fixes: d8e0503 ("CIFS: Add readpage support for SMB2") Cc: stable@vger.kernel.org Signed-off-by: Abdifatah Suruur Reviewed-by: Namjae Jeon Signed-off-by: Paulo Alcantara Signed-off-by: Greg Kroah-Hartman Changed files: fs/smb/client/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=1ba1937de005e261a8858f45bfef5da7458df94c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99272 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99272 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:R/S:U/C:L/I:N/A:H The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H The Best / paranoid CVSS score: 9.1 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: 3 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: 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 alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).