From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98844][MODERATE REGULAR] netfs: clear post-EOF pagecache when extending a file via write [ Upstream Date: Sat, 24 Oct 2026 06:43:12 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98844 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: 3 X-AL-KERNEL-Commit: f8f7d86b3537e885ee620898a38b749fba8a8456 List-Id: CVE: CVE-2026-98844 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: netfs: clear post-EOF pagecache when extending a file via write [ Upstream Commit: f8f7d86b3537e885ee620898a38b749fba8a8456 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f8f7d86b3537e885ee620898a38b749fba8a8456 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98844 Analysis date: Sat, 24 Oct 2026 06:43:12 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: Netfs may expose stale bytes written through an mmap beyond EOF as valid same-file content after a later buffered or direct extending write. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98844 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98844 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-2026-98844 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98844 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=2 LEGACY=MODERATE RESULT=SAME (final reconciliation agrees; DECISION: both 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:N';CWE-226;*CWE-200;*CWE-664;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'A netfs pagecache coherency flaw can leave bytes written through mmap beyond the old EOF and later expose them when an ordinary buffered or direct write extends the file across that region. The demonstrated primitive is stale file data exposure and incorrect file content rather than kernel memory corruption. For the CVSS the PR:L rating is used because reliable triggering normally requires a local process with permission to mmap and write or extend the affected file. Base impact is limited integrity corruption within the folio crossing EOF. The paranoid score also allows limited confidentiality impact if previously hidden bytes become visible to another authorized reader of the same file. The issue is not directly network reachable merely because netfs is used by a network filesystem. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 4.4 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 MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold 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 DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE REMOTE READ OOB LOCK DISK INIT RACE LINUS MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 PrimitiveClass=CLASS_B 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; adds only the technically plausible limited disclosure to another authorized reader. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown * +1 Local unprivileged trigger: ordinary file operations suffice for a user permitted to mmap/write and extend the affected file; host administration is unnecessary. * +1 Important filesystem path: the defect affects netfs page-cache coherency during file extension. * +1 Integrity plausible: stale bytes beyond the old EOF become unintended file content when the file is extended. * Paranoid +1 Confidentiality plausible: those stale bytes may subsequently be visible to another reader authorized for the same file. * No OOB write, UAF, arbitrary kernel write, COW/ownership breach, authorization bypass, protected victim, or kernel crash is shown. * NEW52 B5-R does not apply: there is no retry-accumulated heap OOB write. * NEW53 B3-PENDING does not apply: no write through shared backing into a separately authorized file or victim is established. * B4-PENDING does not apply: no DENY-to-ALLOW authorization decision or omitted security guard exists. 3. Reachability analysis A normal local process with file write/mmap and extension permission can exercise the sequence. No UID 0, capability, namespace privilege, special hardware, race win, or prior host-admin setup is required. Concurrent writers affect the fix’s clamping logic, but concurrency is not required for the basic stale-data condition. 4. Primitive and severity reading The primitive is stale page-cache data surviving beyond EOF and later being reclassified as valid content of the same file. This is a constrained data-lifetime/coherency Class B issue, not kernel memory corruption. Incorrect content is shown; limited same-file disclosure is plausible but cross-user protected-data exposure is not demonstrated. There is no specific ownership or authorization boundary supporting Important retention, so automatic Moderate-range handling remains permissible. 5. One-sentence report phrase Netfs may expose stale bytes written through an mmap beyond EOF as valid same-file content after a later buffered or direct extending write. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm whether affected deployments permit different principals to mmap/write and later read the same network file, which determines whether the limited disclosure has practical cross-user significance. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfs: clear post-EOF pagecache when extending a file via write [ Upstream Commit: f8f7d86b3537e885ee620898a38b749fba8a8456 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f8f7d86b3537e885ee620898a38b749fba8a8456 Changed files: fs/netfs/buffered_write.c fs/netfs/direct_write.c fs/netfs/internal.h fs/netfs/misc.c include/linux/netfs.h 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=f8f7d86b3537e885ee620898a38b749fba8a8456 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98844 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98844 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:L/UI:N/S:U/C:N/I:L/A:N The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N 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: 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: 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).