From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74571][LOW] btrfs: skip global block reserve accounting for rescue mounts [ Upstream Date: Sat, 15 Aug 2026 16:34:08 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74571 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: 076349e4c8d11f6b58c4549976a513b2b4dc6df2 List-Id: CVE: CVE-2026-74571 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: btrfs: skip global block reserve accounting for rescue mounts [ Upstream Commit: 076349e4c8d11f6b58c4549976a513b2b4dc6df2 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=076349e4c8d11f6b58c4549976a513b2b4dc6df2 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74571 Analysis date: Sat, 15 Aug 2026 16:34:08 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate / Low-like Manual review required: YES Summary: A Btrfs rescue mount with corrupted block group tree or raid stripe tree metadata can dereference a NULL root pointer during global block reserve accounting and crash the kernel, but triggering normally requires local administrative mount capability and there is no evidence of memory corruption beyond NULL dereference. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74571 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74571 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74571 LOW 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:N/I:N/A:H';**CWE-476;CWE-754;CWE-703;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 can occur during a Btrfs rescue mount when the block group tree root or raid stripe tree root cannot be read but the corresponding on disk feature bit remains set. btrfs_update_global_block_rsv can then perform global block reserve accounting based on the feature bit and dereference a missing root pointer, causing a kernel crash during mount. For the CVSS the PR:L is used in the paranoid score because some environments may delegate mount capability to a reduced capability root, container root, service account, or storage management process, even though the typical base case requires administrative mount privileges. The issue is not network reachable and requires local ability to mount or influence mounting of a corrupted Btrfs filesystem with rescue options. Impact is denial of service only via kernel crash, with no evidence of UAF, OOB write, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) SKIP CVE-2026-74571 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 8dbfc14fc736eb701089aff09645c3d4ad3decb1 YES NO NO unknown MAYBE LOCK DANGER NULLPTR DISK SKIP IMPROVEONLY INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - 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 Triggered signals: * Reliable kernel crash / strong DoS: +1 The commit shows a reproducible NULL pointer dereference in `btrfs_update_global_block_rsv()` during mount. * Availability impact realistic: +1 The failure is a kernel crash during mount, so the availability impact is system-wide if triggered. * Important filesystem/storage path: +1 The bug is in Btrfs mount and global block reserve accounting, which is a filesystem metadata and mount-time integrity path. Subtracted signals: * Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2 Triggering requires mounting a corrupted Btrfs filesystem with rescue options, which normally requires administrative mount privileges. * Non-default rescue mode / special corrupted filesystem condition: -1 The crash requires `rescue=ibadroots` and a corrupted block group tree root or raid stripe tree root. Paranoid adjustment: * The paranoid score uses a reduced penalty for environments where mount operations are delegated to a reduced-capability root, container root, service account, or storage management process. This raises practical concern slightly but does not make the bug unprivileged in normal deployments. No signals for: * Generic memory corruption * Real lifetime corruption * UAF * OOB write * Privilege escalation * Confidentiality impact * Integrity impact * Network reachability ## 3. Reachability analysis The bug is locally reachable through Btrfs mount processing. In typical deployments, mounting with rescue options requires root or `CAP_SYS_ADMIN`, so the conservative interpretation is privileged local DoS. Namespace or container setups may reduce the practical privilege barrier if a storage management service or container root is allowed to initiate mounts, but this is not the default safe assumption. The path is not network reachable. It also requires a corrupted Btrfs filesystem with specific missing roots while feature bits remain set, plus a read-only rescue mount mode. ## 4. Severity interpretation This behaves like an ordinary Moderate or Low-like kernel DoS issue. The demonstrated primitive is a NULL pointer dereference, not UAF, stale pointer reuse, object replacement, OOB write, arbitrary write, or page-cache corruption. Theoretical impact is limited to crashing the kernel during mount. Realistic exploitation evidence supports DoS only, not privilege escalation or data confidentiality/integrity compromise. ## 5. One-sentence report phrase A Btrfs rescue mount with corrupted block group tree or raid stripe tree metadata can dereference a NULL root pointer during global block reserve accounting and crash the kernel, but triggering normally requires local administrative mount capability and there is no evidence of memory corruption beyond NULL dereference. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: this is a local privileged rescue-mount NULL pointer DoS with special corrupted-filesystem preconditions and no supported UAF, OOB write, information leak, privilege escalation, or network exposure. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: btrfs: skip global block reserve accounting for rescue mounts [ Upstream Commit: 076349e4c8d11f6b58c4549976a513b2b4dc6df2 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=076349e4c8d11f6b58c4549976a513b2b4dc6df2 Changed files: fs/btrfs/block-rsv.c fs/btrfs/disk-io.c fs/btrfs/fs.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=076349e4c8d11f6b58c4549976a513b2b4dc6df2 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74571 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74571 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).