From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74470][MODERATE 7.0] scsi: scsi_debug: Fix REPORT ZONES alloc_len underflow OOB write Date: Sat, 15 Aug 2026 17:43:10 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74470 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 49e5b25a0b74dbac595f122e5608fdce2918cc4e List-Id: CVE: CVE-2026-74470 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: scsi: scsi_debug: Fix REPORT ZONES alloc_len underflow OOB write Commit: 49e5b25a0b74dbac595f122e5608fdce2918cc4e Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49e5b25a0b74dbac595f122e5608fdce2918cc4e Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74470 Analysis date: Sat, 15 Aug 2026 17:43:10 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A crafted REPORT ZONES allocation length in scsi_debug can cause a 4 GB allocation size to truncate to kzalloc(0) on 32-bit systems, leading to an out-of-bounds write and likely local kernel crash when raw SCSI command access is available. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74470 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74470 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-2026-74470 MODERATE 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:L/I:L/A:H';*CWE-787;CWE-190;CWE-131;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.6';DESCR 'scsi_debug REPORT ZONES can compute a 4 GB response buffer length from a large alloc_len value on 32-bit systems. The 4 GB size can truncate to 0 for kzalloc, so kzalloc(0) returns ZERO_SIZE_PTR and later descriptor writes are made past that pointer in resp_report_zones. A local actor that can issue raw SCSI commands to an affected scsi_debug zoned device can trigger a kernel OOB write and likely panic. For the CVSS the PR:L is used in the paranoid score because reliable triggering may only require local access to the scsi_debug device or an account allowed to send SG_IO style commands, while loading or configuring the debug device itself is usually administrative. The issue is not network reachable. Impact is at least local denial of service via kernel crash, and in the paranoid interpretation may include limited confidentiality or integrity impact because the failure mode is an OOB write rather than a pure NULL dereference.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES WRITE OOB DANGER LOG HARDWARE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum** ## 2. Signal breakdown Paranoid score signals: * Local unprivileged trigger: +1 If scsi_debug is already loaded and the device node allows SG_IO or raw SCSI command access, a local non-root user may be able to issue REPORT ZONES with a crafted allocation length. * Generic memory corruption: +2 The patch description explicitly states out-of-bounds write / panic. This is not just a warning or validation cleanup. * Memory layout invariant restoration: +1 The fix restores consistency between alloc_len, rep_max_zones, arr_len, and the real device zone count. * Reliable kernel crash / strong DoS: +1 kzalloc(0) returns ZERO_SIZE_PTR, then desc = arr + 64 is written through, making panic/Oops realistic. * Weak LPE concern: +1 The primitive is an OOB write, so manual review is justified, but there is no demonstrated reclaim, controlled target, arbitrary write, or object replacement. * Integrity impact plausible: +1 Limited integrity concern is defensible because the failure mode is an OOB write, not a pure NULL dereference. Subtract: * Corruption primitive constrained / no attacker-controlled target: -1 The overwrite appears near ZERO_SIZE_PTR and the payload is mostly kernel-generated report-zone descriptor data. * Rare / non-default condition: -1 Requires 32-bit truncation behavior and scsi_debug zoned REPORT ZONES exposure. scsi_debug is a debug/test driver, not a default production storage path. Conservative score is lower because loading/configuring scsi_debug normally requires administrative privileges. ## 3. Reachability analysis The bug is local, not network reachable. In the conservative deployment model, triggering requires root or administrative control to load and configure scsi_debug, so the issue is lower priority. In the paranoid model, if an affected scsi_debug zoned device already exists and local users can issue SG_IO-style commands to it, PR:L is reasonable. Namespaces do not automatically make this reachable, but container or service configurations that expose raw SCSI devices could lower the practical privilege requirement. Call-site confidence: high, because the vulnerable allocation and later descriptor write are described directly in the patch context. ## 4. Severity interpretation This is not a Strong Important candidate by default because the affected driver is non-default/debug-oriented, the condition is 32-bit-specific, and the OOB write appears highly constrained. However, it should not be auto-closed as an ordinary low-risk DoS because the patch documents an explicit kernel OOB write, not only a crash or resource leak. Realistic impact is likely local kernel crash. Theoretical impact beyond DoS is limited but deserves manual review due to memory corruption semantics. ## 5. One-sentence report phrase A crafted REPORT ZONES allocation length in scsi_debug can cause a 4 GB allocation size to truncate to kzalloc(0) on 32-bit systems, leading to an out-of-bounds write and likely local kernel crash when raw SCSI command access is available. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: explicit OOB write candidate, PR:L is plausible when the debug device is already exposed, and paranoid scoring reaches actionable Moderate even though practical exploitation beyond DoS is constrained. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: scsi: scsi_debug: Fix REPORT ZONES alloc_len underflow OOB write Commit: 49e5b25a0b74dbac595f122e5608fdce2918cc4e Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49e5b25a0b74dbac595f122e5608fdce2918cc4e Commit description: resp_report_zones() sizes the reply buffer from the CDB allocation length. The v3 fix rounds alloc_len up with ALIGN() before deriving the descriptor count: rep_max_zones = (ALIGN((u64)alloc_len, RZONES_DESC_HD) - RZONES_DESC_HD) >> ilog2(RZONES_DESC_HD); arr_len = (u64)RZONES_DESC_HD * (rep_max_zones + 1); For alloc_len in 0xFFFFFFC1..0xFFFFFFFF, ALIGN() rounds up to 0x100000000, so arr_len is 4 GB. On 32-bit, kzalloc()'s size_t is 32-bit and truncates 0x100000000 to 0; kzalloc(0) returns ZERO_SIZE_PTR, which passes the !arr check, and desc = arr + 64 is then dereferenced in the loop -> out-of-bounds write / panic. Clamp rep_max_zones to devip->nr_zones. The loop already stops at sdebug_capacity (after nr_zones zones), so a report can never hold more than nr_zones descriptors; the clamp does not change the report, it only bounds arr_len to (nr_zones + 1) * RZONES_DESC_HD, a real device property that can never reach 0x100000000. Fixes: 7db0e0c ("scsi: scsi_debug: Fix buffer size of REPORT ZONES command") Suggested-by: Damien Le Moal Cc: stable@vger.kernel.org Signed-off-by: Ibrahim Hashimov Assisted-by: AuditCode-AI:2026.07 Reviewed-by: Damien Le Moal Reviewed-by: Bart Van Assche Link: https://patch.msgid.link/20260712183739.83915-1-security@auditcode.ai Signed-off-by: Martin K. Petersen Signed-off-by: Greg Kroah-Hartman Changed files: drivers/scsi/scsi_debug.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=49e5b25a0b74dbac595f122e5608fdce2918cc4e ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74470 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74470 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:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 6.6 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: 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: NO 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).