From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64187][LOW] xfs: fail recovery on a committed log item with no regions Date: Mon, 20 Jul 2026 13:03:32 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64187 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: 2 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: d50b1fd066d66ceb548ba43e332cfe8a47e5e55a List-Id: CVE: CVE-2026-64187 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: xfs: fail recovery on a committed log item with no regions Commit: d50b1fd066d66ceb548ba43e332cfe8a47e5e55a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d50b1fd066d66ceb548ba43e332cfe8a47e5e55a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64187 Analysis date: Mon, 20 Jul 2026 13:03:32 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64187 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64187 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-2026-64187 LOW CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in the XFS log recovery path can occur when a crafted committed log item contains no regions, leaving ri_cnt as 0 and ri_buf as NULL during recovery. Mounting or recovering such a crafted XFS filesystem can crash the kernel when xlog_recover_reorder_trans tries to inspect the log item type. For the CVSS the PR:L is used for the paranoid score because some environments delegate mount or storage image handling to less privileged users, container root, service accounts, or automation even though normal XFS mounting usually requires CAP_SYS_ADMIN. The issue is not network reachable by itself and requires the crafted filesystem or log to be processed locally. Impact is denial of service via kernel crash, with no concrete evidence of information disclosure or privilege escalation from this patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) YES KASAN NULLPTR DISK LOG LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 1. ActionableScore * Conservative score: 1 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: 2. Signal breakdown * Reliable kernel crash / strong DoS: +1. The patch and KASAN trace show a NULL pointer dereference in `xlog_recover_reorder_trans()` during XFS log recovery. * Important filesystem/storage path: +1. The bug is in XFS journal/log recovery during mount. * Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2 conservative. Mounting an XFS filesystem normally requires administrative privileges. * Local delegated or automated mount exposure: +1 paranoid only. Some environments may process filesystem images through container root, service accounts, removable media workflows, or storage automation. * No generic memory corruption signal. The concrete primitive is NULL pointer dereference from `ri_buf == NULL`, not UAF, OOB write, double free, type confusion, or page-cache corruption. * No confidentiality or integrity signal. The patch does not show disclosure, writable stale object access, metadata overwrite, or privilege escalation primitive. 3. Reachability analysis A crafted XFS log is required, and the vulnerable path is reached when the filesystem is mounted and log recovery runs. In normal deployments this requires CAP_SYS_ADMIN or equivalent mount privileges, so conservative reachability is local privileged. Namespaces or containerized environments can lower practical exposure only if a reduced-privilege actor can cause the host or a privileged service to mount or recover attacker-supplied XFS images. The path is not network reachable by itself. 4. Severity interpretation This behaves like an ordinary local DoS rather than an Important-class vulnerability. The theoretical issue is in a filesystem recovery parser, but the demonstrated failure mode is a NULL pointer dereference and immediate crash. There is no evidence of attacker-controlled reclaim, stale object reuse, write-after-free, arbitrary write, page-cache corruption, or a practical privilege escalation path. 5. One-sentence report phrase A crafted XFS recovery log with a committed log item containing no regions can trigger a NULL pointer dereference during mount recovery, causing a local kernel crash when the malformed filesystem is processed. 6. Manual review recommendation NO MANUAL CHECK NEEDED. This can be auto-closed for normal environments because it is a crafted-filesystem local DoS requiring mount/recovery privileges and does not show a memory corruption or privilege escalation primitive. Review only if the product automatically mounts untrusted XFS media or delegates filesystem image mounting to reduced-privilege users. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: xfs: fail recovery on a committed log item with no regions Commit: d50b1fd066d66ceb548ba43e332cfe8a47e5e55a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d50b1fd066d66ceb548ba43e332cfe8a47e5e55a Commit description: If the first op of a transaction is a bare transaction header (len == sizeof(struct xfs_trans_header)), xlog_recover_add_to_trans() adds an item but no region, leaving it on r_itemq with ri_cnt == 0 and ri_buf == NULL. The header can be split across op records, so later ops may still add regions; the item is only invalid if the transaction commits with none. The runtime commit path never emits such a transaction, so this only happens on a crafted log. It came from an AI-assisted code audit of the recovery parser. xlog_recover_reorder_trans() calls ITEM_TYPE() on the item, which reads *(unsigned short *)item->ri_buf[0].iov_base and faults on the NULL ri_buf. Reject it there, before the commit handlers that also read ri_buf[0]. KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:xlog_recover_reorder_trans (fs/xfs/xfs_log_recover.c:1836) xlog_recover_commit_trans (fs/xfs/xfs_log_recover.c:2043) xlog_recover_process_data (fs/xfs/xfs_log_recover.c:2501) xlog_do_recovery_pass (fs/xfs/xfs_log_recover.c:3244) xlog_recover (fs/xfs/xfs_log_recover.c:3493) xfs_log_mount (fs/xfs/xfs_log.c:618) xfs_mountfs (fs/xfs/xfs_mount.c:1034) xfs_fs_fill_super (fs/xfs/xfs_super.c:1938) vfs_get_tree (fs/super.c:1695) path_mount (fs/namespace.c:4161) __x64_sys_mount (fs/namespace.c:4367) Fixes: 89cebc8 ("xfs: validate transaction header length on log recovery") Cc: stable@vger.kernel.org # v4.3 Reported-by: Xiang Mei Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Weiming Shi Reviewed-by: Christoph Hellwig Reviewed-by: "Darrick J. Wong" Signed-off-by: Carlos Maiolino Signed-off-by: Greg Kroah-Hartman Changed files: fs/xfs/xfs_log_recover.c fs/xfs/xfs_log.c fs/xfs/xfs_mount.c fs/xfs/xfs_super.c fs/super.c fs/namespace.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=d50b1fd066d66ceb548ba43e332cfe8a47e5e55a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64187 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64187 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:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: 2 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).