From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98403][MODERATE 7.0] s390/boot: Avoid IPL parameter append past command line [ Upstream Date: Wed, 14 Oct 2026 23:04:08 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98403 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: 5 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: af9866021a00ab9eeacf0c33ee73f3d134b4ed70 List-Id: CVE: CVE-2026-98403 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: s390/boot: Avoid IPL parameter append past command line [ Upstream Commit: af9866021a00ab9eeacf0c33ee73f3d134b4ed70 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af9866021a00ab9eeacf0c33ee73f3d134b4ed70 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98403 Analysis date: Wed, 14 Oct 2026 23:04:08 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98403 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98403 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-2026-98403 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98403 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-191;CWE-125;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H';BEST CVSS score: '6.7';DESCR 'An out of bounds write can occur during s390 early boot when early_command_line occupies all available space except for its terminating byte. append_ipl_block_parm() then passes a zero destination size and a pointer beyond the command line buffer to an IPL parameter conversion helper. The helper subtracts one from the unsigned size, producing a very large effective bound and allowing converted IPL parameter data to overwrite adjacent boot memory. The demonstrated impact includes corruption of boot data, altered boot behavior, or failure to boot. The broader confidentiality and integrity impact depends on the affected memory layout and is not proven as a practical privilege escalation. For the CVSS the PR:H value is used because reliable triggering normally requires administrative control over the s390 boot command line or IPL parameter block. The issue is not directly network reachable and executes before normal userspace starts. Impact is at least denial of service and boot state corruption. The actual out of bounds write supports a paranoid CIA:HHH assessment and requires manual review. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6.7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. 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 has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 0 with primitive class CLASS_B and manual review RECOMMENDED. 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 Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE SIMPLEFIX HARDWARE KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=YES NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw conservative score: 1 * Conservative score: 5 * Raw paranoid score: 1 * Paranoid score: 5 * Applied conservative floor: 1 -> 5 under the Manual Review Safety Floor for a concrete attacker-influenced kernel out-of-bounds write. * Applied paranoid floor: 1 -> 5 for the same established primitive. No speculative exploitation bonus was added. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 Strong corruption primitive. A zero size undergoes unsigned subtraction, after which an IPL-derived parameter is written starting one byte beyond `early_command_line`. This is a confirmed OOB write, not a hypothetical bounds concern. * +1 Strong DoS. Corruption occurs during early boot and can corrupt adjacent boot state or prevent successful boot. * -2 Full host-admin-equivalent prerequisite. Triggering requires control over the s390 boot command line and IPL parameter block before normal userspace starts. * No race penalty. The faulty sequence is deterministic once the command line is full and an IPL parameter is processed. * No confidentiality or separate integrity bonus. The adjacent victim, disclosure path, protected state, and privilege-escalation consequence are not established. * No arbitrary or directed write bonus. The starting address is fixed relative to `early_command_line`, and arbitrary target selection is not shown. * No UAF, reclaim, callback, refcount, or lifetime primitive exists. * B5-R does not apply. No retry or re-entry accumulated index is present. * B3-PENDING does not apply. No shared backing or COW ownership violation exists. * B4-PENDING does not apply. No authorization decision changes from DENY to ALLOW. Raw arithmetic: `+2 +1 -2 = 1`. 3. Reachability analysis The vulnerable operation executes only during s390 early boot. The relevant actor must provide both a command line occupying all but the terminating byte and an IPL parameter that reaches the conversion helper. This is machine, partition, or guest boot administration rather than an ordinary runtime-user interface. Host-admin-equivalent control is therefore positively established for the affected kernel instance. Numeric host UID 0 is not necessarily the actor because IPL configuration may be supplied through platform or virtualization management, so `RequiresHostUID0` remains UNKNOWN. No namespace-scoped path, network trigger, runtime ioctl, race, or ordinary local-user path is present. s390 is architecture-specific, but no additional rarity penalty is applied because architecture specialization alone is insufficient. 4. Primitive and severity interpretation The exact primitive is a sequential attacker-influenced OOB write into memory following a static early-boot command-line buffer. `COMMAND_LINE_SIZE - len - 1` becomes zero, the helper subtracts one from the unsigned size, and converted IPL bytes are written beyond the destination. This is CLASS_A because an actual input-influenced OOB write is established. It is not a UAF and does not involve stale storage, cleanup, repeated release, or refcount mutation. The supported practical consequences are adjacent boot-state corruption and failure to boot. Broader corruption is technically possible because the helper receives an effectively huge bound, but no specific adjacent object, arbitrary target, disclosure, LPE, or post-boot exploitation chain is demonstrated. `ImportantCandidate=YES` and `AutoDowngradeAllowed=NO` preserve the concrete write primitive for review. The strong host-administration prerequisite substantially limits practical attacker value, so the operational assessment remains Actionable Moderate unless layout analysis identifies a meaningful security boundary or controllable adjacent target. 5. One-sentence report phrase A full s390 boot command line causes an unsigned size underflow that lets IPL parameter conversion write beyond `early_command_line`, creating a host-admin-triggered early-boot memory corruption and denial-of-service condition. 6. Manual review recommendation MANUAL CHECK REQUIRED Review the linker layout after `early_command_line`, the maximum converted IPL parameter length and content control, and whether any deployment permits a less-privileged partition or guest-management actor to supply the complete trigger. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: s390/boot: Avoid IPL parameter append past command line [ Upstream Commit: af9866021a00ab9eeacf0c33ee73f3d134b4ed70 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af9866021a00ab9eeacf0c33ee73f3d134b4ed70 Changed files: arch/s390/boot/ipl_parm.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=af9866021a00ab9eeacf0c33ee73f3d134b4ed70 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98403 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98403 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:H/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 6.7 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: 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 alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).