From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98636][LOW] squashfs: Add dictionary size range check to prevent shift-out-of-bounds [ Upstream Date: Sat, 24 Oct 2026 08:17:00 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98636 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 0 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: b02948a23455f8190a53887b2d2c13ae1d360cea List-Id: CVE: CVE-2026-98636 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: squashfs: Add dictionary size range check to prevent shift-out-of-bounds [ Upstream Commit: b02948a23455f8190a53887b2d2c13ae1d360cea Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b02948a23455f8190a53887b2d2c13ae1d360cea Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98636 Analysis date: Sat, 24 Oct 2026 08:17:00 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A host-privileged mount of a malformed SquashFS image can trigger an invalid negative shift, potentially escalating a UBSAN warning to a kernel panic under configured warning escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98636 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98636 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: LOW 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-2026-98636 LOW https://www.kernelcve.org/list/?q=CVE-2026-98636 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=LOW RESULT=DIFF (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';CWE-1335;*CWE-20;CWE-369;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'A malformed SquashFS image with COMP_OPTS enabled and a zero XZ dictionary size makes ffs return zero and produces a negative shift exponent in squashfs_xz_comp_opts. This is undefined shift behavior and may produce a UBSAN warning or a kernel panic when warning escalation is configured. The code does not provide an OOB access, UAF, arbitrary write, or information disclosure primitive, so confidentiality and integrity remain unaffected. For the CVSS the PR:H value is selected because reliable direct triggering normally requires authority to mount a SquashFS image. The issue is local and is not triggered merely by reading or storing the image. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 4.4 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage IMPORTANT to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation 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 LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE WRITE OOB DISK SIMPLEFIX IMPROVEONLY LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=YES NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: -2. * Conservative score: 0 after applying the score-range minimum. * Raw paranoid score: -1. * Paranoid score: 0 after applying the score-range minimum. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * **-2 host-admin-equivalent privilege:** Direct parsing requires mounting the malformed SquashFS image. SquashFS is not normally user-namespace mountable, so this requires init-user-namespace `CAP_SYS_ADMIN` or an equivalent privileged actor. * **+0 invalid shift:** `ffs(0) - 1` produces `n == -1`, followed by shifts with an invalid exponent. This is undefined arithmetic behavior, not a demonstrated memory access. * **Paranoid +1 possible kernel crash:** UBSAN can report the invalid shift, and warning escalation can turn that report into a panic. This is configuration-dependent, so it is not included in the conservative score. * No OOB read/write, UAF, corrupted active object, disclosure, authorization bypass, or persistent integrity effect is shown. * NEW52/B5-R does not apply: there is no heap OOB write, retry-accumulated index, or downstream consumption of corrupted structured state. * No additional availability point is awarded beyond the paranoid panic possibility. 3. Reachability analysis The malformed dictionary size is attacker-controlled through the filesystem image, but parsing occurs during mount. The complete direct trigger therefore requires host-level mount authority; merely storing or reading the image is insufficient. Numeric host UID 0 is not intrinsically required because the relevant authority is `CAP_SYS_ADMIN`. No namespace-scoped mounting path, prior attacker-accessible mount, special hardware, or race is evidenced. 4. Primitive and severity reading The exact defect is an invalid negative shift exponent caused by accepting a zero XZ dictionary size. It is neither active structured-state corruption nor stale storage. `PrimitiveClass=CLASS_C` reflects invalid-state behavior with a configuration-dependent panic possibility. Stronger memory-corruption or non-crash leverage is unsupported. Important review preservation does not apply, and automatic downgrade is safe. 5. One-sentence report phrase A host-privileged mount of a malformed SquashFS image can trigger an invalid negative shift, potentially escalating a UBSAN warning to a kernel panic under configured warning escalation. 6. Manual review advice NO MANUAL CHECK NEEDED The patch shows a narrow validation defect without memory corruption, authorization bypass, or below-host-admin reachability. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: squashfs: Add dictionary size range check to prevent shift-out-of-bounds [ Upstream Commit: b02948a23455f8190a53887b2d2c13ae1d360cea Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b02948a23455f8190a53887b2d2c13ae1d360cea Changed files: fs/squashfs/xz_wrapper.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=b02948a23455f8190a53887b2d2c13ae1d360cea ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98636 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98636 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:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.4 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: 0 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).