From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64216][MODERATE 7.0] netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages() [ Upstream Date: Fri, 24 Jul 2026 12:27:49 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64216 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: 4 X-AL-KERNEL-Commit: 6080fa3ecfbb4448a3b47368629534c09b6ec750 List-Id: CVE: CVE-2026-64216 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages() [ Upstream Commit: 6080fa3ecfbb4448a3b47368629534c09b6ec750 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6080fa3ecfbb4448a3b47368629534c09b6ec750 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64216 Analysis date: Fri, 24 Jul 2026 12:27:49 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A potential UAF in netfs abandoned read cleanup can occur when cleanup code dereferences a folio after ownership has returned to the caller, allowing a local user with access to an affected mounted netfs filesystem to potentially trigger a kernel crash and requiring manual review for memory corruption risk. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64216 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64216 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-2026-64216 MODERATE CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'netfs has a potential UAF in abandoned read cleanup because netfs_unlock_abandoned_read_pages() and netfs_unlock_read_folio() compared folio index after ownership of the protected folio had returned to the caller. A local user able to exercise buffered write or write begin paths on a mounted netfs filesystem may be able to trigger the race under error or abandoned read conditions, causing a kernel crash and possible memory corruption. For the CVSS the PR:L is used because triggering requires local code or process access to files on the affected mounted filesystem, not administrative privileges. The issue is not directly network reachable as a packet attack, although it depends on network filesystem code paths. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality and integrity impact due to UAF related memory corruption, so manual review is recommended.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) SKIP CVE-2026-64216 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: ee4cdf7ba857a894ad1650d6ab77669cbbfa329e YES NO NO unknown MAYBE REMOTE WRITE OOB DISK UAF LINUS KPANIC KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum** ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1 A local user can potentially exercise buffered write or write begin paths on an already mounted netfs-backed filesystem. Mount setup may require privilege, but file access on an existing mount often does not. * Memory corruption, weak/indirect corruption candidate: +1 The patch explicitly fixes a potential UAF, but the shown primitive is a stale folio dereference for `folio->index`, not a demonstrated write-after-free, callback dispatch, type confusion, or attacker-controlled reclaim. * Real lifetime corruption: +1 The root issue is ownership/lifetime mismatch. After `NETFS_RREQ_IN_PROGRESS` is cleared, ownership of the protected folio returns to the caller, but cleanup code could still dereference it. * Availability impact realistic: +1 A stale folio dereference can plausibly crash the kernel or corrupt state enough to cause local DoS, especially under abandoned read or error cleanup paths. * Important filesystem/storage path: +1 This is in netfs buffered read/write and folio handling, affecting page-cache-adjacent filesystem I/O paths. Negative signals: * Hard or unreliable race / special timing required: -1 Triggering depends on a narrow lifetime window around abandoned read cleanup and caller ownership transfer. Paranoid-only signal: * Weak LPE concern from explicit UAF lifetime bug: +1 The patch context explicitly states potential UAF on a folio object. There is no demonstrated reclaim or write primitive, so this is not strong LPE plausibility, but it is enough to avoid auto-close and require manual review. ## 3. Reachability analysis The bug is locally reachable through filesystem operations on a mounted netfs filesystem, especially buffered write or write-begin paths that perform read-before-write or prefetch behavior. It is not directly network-triggerable as a packet parsing issue, even though netfs may be backed by network filesystems such as NFS, CIFS, AFS, or similar users. Namespaces and containers may matter if an untrusted workload has access to an already mounted affected filesystem. Creating or configuring such mounts may require privileges, but ordinary file access may be enough for the relevant data path once the mount exists. Call-site confidence: high. The patch includes both the setup sites that store `no_unlock_folio` and the cleanup sites that compare it. ## 4. Severity interpretation This behaves more like an actionable Moderate than an ordinary Moderate because the patch explicitly addresses a potential UAF in folio lifetime handling. The realistic demonstrated impact is local DoS or kernel crash. The theoretical worst case includes memory corruption from stale folio access, but the patch does not show attacker-controlled reclaim, type confusion, arbitrary write, or callback control. This should not be treated as a strong Important candidate without additional exploitability evidence, but it should also not be auto-closed as a low-risk cleanup. ## 5. One-sentence report phrase A potential UAF in netfs abandoned read cleanup can occur when cleanup code dereferences a folio after ownership has returned to the caller, allowing a local user with access to an affected mounted netfs filesystem to potentially trigger a kernel crash and requiring manual review for memory corruption risk. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch explicitly fixes a potential UAF in folio lifetime handling. Even though the currently visible primitive is weak and race-dependent, kernel folio and page-cache ownership bugs have enough escalation history to require source-level manual review rather than auto-close. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages() [ Upstream Commit: 6080fa3ecfbb4448a3b47368629534c09b6ec750 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6080fa3ecfbb4448a3b47368629534c09b6ec750 Changed files: fs/netfs/buffered_read.c fs/netfs/read_collect.c fs/netfs/read_retry.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=6080fa3ecfbb4448a3b47368629534c09b6ec750 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64216 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64216 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:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 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: 4 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).