From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80899][MODERATE REGULAR] erofs: remove fscache backend entirely [ Upstream Date: Fri, 04 Sep 2026 14:27:34 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80899 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: f6145794f17a27d25f8a84edb80731fb0e07c196 List-Id: CVE: CVE-2026-80899 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: erofs: remove fscache backend entirely [ Upstream Commit: f6145794f17a27d25f8a84edb80731fb0e07c196 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6145794f17a27d25f8a84edb80731fb0e07c196 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80899 Analysis date: Fri, 04 Sep 2026 14:27:34 -0400 ActionableScore: 4 ActionableScore lower bound: 1 Actionable bucket: Borderline manual review recommended / Actionable Moderate only if external issues confirm a concrete primitive Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80899 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80899 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-2026-80899 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80899 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-664;CWE-703;CWE-693;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.8';DESCR 'The affected area is the deprecated EROFS over fscache on demand read backend, which was used for lazy image pulling through fscache and cachefiles integration. The visible diff does not show a concrete UAF, OOB write, arbitrary write, or information leak primitive, so the base impact is limited and mainly represents possible local denial of service or incorrect behavior when the feature is enabled. For the CVSS the PR:L is used for the paranoid score because delegated mount workflows, container image services, or reduced capability root contexts may expose this path without full host administrator control. The issue is not directly network reachable as packet traffic, but it may be reachable through a local or internal image management workflow where EROFS fscache based lazy pulling is used. Impact is at least availability risk in affected deployments and in the worst still defensible case may include limited confidentiality or integrity impact due to unspecified implementation issues. YES REQUIRES MANUAL CHECK.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate only if external issues confirm a concrete primitive (with actual score 3) YES DISK HARDWARE INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=1 1. ActionableScore * Conservative score: 1 * Paranoid score: 4 * Final recommended bucket: **Borderline manual review recommended / Actionable Moderate only if external issues confirm a concrete primitive**:: 2. Signal breakdown * +1 Important filesystem/storage path. EROFS fscache on demand is in filesystem data access and cache integration paths. * +1 Availability impact plausible. The backend removal is explicitly motivated by newly found implementation issues, but the supplied diff does not show a concrete crash path. * +1 Cross mount shared cache boundary concern, paranoid only. The removed feature involved trusted domain IDs, shared blobs, fscache, cachefiles, and page cache sharing across mounts. This is a policy sensitive area, but no concrete bypass is proven in the pasted patch. * +1 Local reduced privilege trigger concern, paranoid only. In Nydus or container image lazy pulling deployments, a reduced privilege service or delegated workflow may expose this path without full host administrator intent. * +1 Filesystem image and cache input control concern, paranoid only. Attackers may influence image contents or lazy pull inputs in some deployments, but the patch does not show a specific memory corruption primitive. * -1 Deprecated and non default feature. EROFS_FS_ONDEMAND was deprecated for almost two years and must be enabled and used. * Conservative subtraction: -2 for typical CAP_SYS_ADMIN or root controlled mount and configuration requirements. 3. Reachability analysis Typical direct triggering requires EROFS fscache on demand support to be built and used, likely through privileged mount or container image infrastructure. It is not directly network reachable as packet processing. Namespaces and container workflows matter because Nydus style lazy pulling may let less privileged tenants influence images or pull behavior through a privileged service, but that is deployment dependent. The supplied patch removes a deprecated backend rather than fixing a visible UAF, OOB write, arbitrary write, or info leak. 4. Severity interpretation This does not qualify as a Strong Important candidate from the provided patch alone. It is better treated as borderline manual review material because the affected code is a filesystem/storage cache backend with cross mount sharing semantics and the commit references external implementation issues. Theoretical impact could exceed ordinary DoS if those external issues involve cache ownership, lifetime, or page sharing bugs, but realistic evidence in the pasted diff is insufficient to score it as proven memory corruption or privilege escalation. 5. One-sentence report phrase The deprecated EROFS fscache on demand backend was removed after newly found implementation issues in a filesystem cache and lazy image pulling path, with practical risk depending on whether EROFS_FS_ONDEMAND or Nydus style workflows are enabled. 6. Manual review recommendation YES REQUIRES MANUAL CHECK. MANUAL CHECK REQUIRED. The visible diff does not prove a concrete exploit primitive, but the full backend removal and external issue references make this unsuitable for automatic closure without checking the linked reports and affected deployment usage. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: erofs: remove fscache backend entirely [ Upstream Commit: f6145794f17a27d25f8a84edb80731fb0e07c196 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6145794f17a27d25f8a84edb80731fb0e07c196 Changed files: fs/erofs/data.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=f6145794f17a27d25f8a84edb80731fb0e07c196 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80899 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80899 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:H/PR:H/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 5.8 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: 1 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 alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).