From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64567][MODERATE 7.0] btrfs: reject free space cache with more entries than pages [ Upstream Date: Wed, 05 Aug 2026 05:06:26 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64567 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: 33878ba25e2638bc0c61623d7a05c9ca2b74c039 List-Id: CVE: CVE-2026-64567 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: btrfs: reject free space cache with more entries than pages [ Upstream Commit: 33878ba25e2638bc0c61623d7a05c9ca2b74c039 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=33878ba25e2638bc0c61623d7a05c9ca2b74c039 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64567 Analysis date: Wed, 05 Aug 2026 05:06:26 -0400 ActionableScore: 5 ActionableScore lower bound: 1 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64567 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64567 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-2026-64567 MODERATE CHECK WITH IMPACT FROM ORIG NN NONE 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:N/A:H';CWE-125;CWE-129;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.1';DESCR 'A malformed Btrfs v1 free space cache can advertise more entries than the cache inode size can back with pages. During cache load, io_ctl_check_crc can access io_ctl pages beyond the allocated pages array and the out-of-bounds value may then be treated as a struct page, leading to a general protection fault or kernel crash. For the CVSS the PR:L is used in the paranoid score because some deployments allow a local user, container root, desktop automount path, or helper service to cause mounting of user supplied filesystem images. The issue is not network reachable and requires a crafted local filesystem image or corrupted on-disk metadata. Impact is at least local denial of service via kernel crash. A limited confidentiality impact is kept only for paranoid triage because the primitive is an out-of-bounds kernel heap read, while privilege escalation is not strongly supported by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 3) YES READ KASAN OOB DISK SKIP IMPROVEONLY MEMORY INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=1 1. ActionableScore * Conservative score: 1 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum** 2. Signal breakdown * Memory corruption, Weak/indirect corruption candidate: +1. The bug is an OOB read from `io_ctl->pages[index]`, and the out-of-bounds value may be interpreted as a `struct page`. No OOB write or attacker-controlled overwrite is shown. * Reliable kernel crash / strong DoS: +1. The commit provides a KASAN slab-out-of-bounds report followed by GP fault behavior. * Important filesystem/storage path: +1. This is Btrfs filesystem metadata parsing during free space cache load. * Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. Mounting crafted Btrfs images normally requires privileged mount capability. * Paranoid local unprivileged trigger: +1. Some environments may expose mounting through desktop automount, helper services, container root, or delegated mount paths. * Filesystem/storage metadata corruption reachable by an unprivileged local user: +1 in paranoid scoring only. This applies if an unprivileged user can cause a crafted filesystem image to be mounted. * No strong LPE signal. The patch shows OOB read and crash, not reclaim, overwrite, callback control, type confusion, or arbitrary write. * No remote/network signal. The trigger requires local crafted filesystem metadata. 3. Reachability analysis A typical attacker needs the ability to provide or modify a Btrfs filesystem image and cause the kernel to load its v1 free space cache. In normal server deployments this usually means CAP_SYS_ADMIN or equivalent mount privilege, so the conservative score is low. In less strict environments, a local user may influence mounting through automount, removable media handling, container root workflows, or privileged helper services, which justifies the paranoid PR:L interpretation. The affected code is not network reachable. The path is storage metadata parsing and is realistic only when malformed Btrfs metadata is mounted or otherwise loaded. 4. Severity interpretation This behaves like an actionable Moderate issue rather than a clear Important-class vulnerability. The demonstrated impact is a local kernel crash from an out-of-bounds kernel heap read and bogus `struct page` interpretation. Theoretical confidentiality concern exists because the primitive is an OOB read, but there is no demonstrated disclosure path, no write primitive, and no strong privilege escalation evidence. Manual review is still recommended because filesystem metadata parsers have historically produced underestimated impact when reachable by untrusted local users. 5. One-sentence report phrase A malformed Btrfs v1 free space cache can make the kernel read past the allocated `io_ctl->pages` array during cache loading, causing a GP fault or kernel crash when a crafted filesystem image is mounted. 6. Manual review recommendation MANUAL CHECK REQUIRED. This is a kernel memory safety issue in a filesystem metadata parser with a demonstrated OOB read and crash, and the practical priority depends strongly on whether untrusted users can trigger mounting of crafted Btrfs images. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: btrfs: reject free space cache with more entries than pages [ Upstream Commit: 33878ba25e2638bc0c61623d7a05c9ca2b74c039 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=33878ba25e2638bc0c61623d7a05c9ca2b74c039 Changed files: fs/btrfs/free-space-cache.c fs/btrfs/block-group.c fs/btrfs/async-thread.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=33878ba25e2638bc0c61623d7a05c9ca2b74c039 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64567 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64567 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:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H The Best / paranoid CVSS score: 6.1 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: 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: NO 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).