From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89602][MODERATE 7.0] erofs: skip sufficiently large global buffers when resizing [ Upstream Date: Sat, 12 Sep 2026 05:29:26 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89602 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: unknown X-AL-KERNEL-Commit: 7267557ce98ccd07faaf3bc86382448950cc4ff6 List-Id: CVE: CVE-2026-89602 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: erofs: skip sufficiently large global buffers when resizing [ Upstream Commit: 7267557ce98ccd07faaf3bc86382448950cc4ff6 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7267557ce98ccd07faaf3bc86382448950cc4ff6 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89602 Analysis date: Sat, 12 Sep 2026 05:29:26 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89602 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89602 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-2026-89602 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89602 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-787;CWE-122;CWE-131;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'An EROFS global buffer resize retry can allocate a temporary page pointer array that is smaller than the already grown gbuf nrpages value and then copy more existing pointers than the array can hold. This creates a heap out of bounds write in fs/erofs/zutil.c after a partial resize failure followed by a retry with an intermediate size. For the CVSS the PR:L is used because a local user may be able to trigger EROFS decompression or buffer growth on an already mounted filesystem and may also influence memory pressure, although environments that require a privileged mount of a crafted image may justify PR:H or UI:R. The issue is not network reachable. Impact is at least local denial of service via memory corruption and kernel crash, and in the paranoid case may include confidentiality or integrity impact because the primitive is an out of bounds heap write involving kernel page pointer arrays.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) SKIP CVE-2026-89602 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE DISK SIMPLEFIX LINUS KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_B RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 5 * Conservative score: 5 * Raw paranoid score: 5 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: No floor or cap changed the score. 2. Signal breakdown Positive signals: * +1 Constrained kernel buffer overwrite. The commit explicitly says that retrying an intermediate size allocates a temporary pointer array smaller than gbuf->nrpages and then copies more existing pointers than the array can hold. * +1 Memory layout invariant restoration. The bug is an allocation-size vs copy-size mismatch in z_erofs_gbuf_growsize(), where nrpages can be smaller than the already grown buffer size. * +1 Reliable kernel crash / strong DoS. A heap out-of-bounds write of page pointers in kernel memory can realistically corrupt adjacent heap state and crash the kernel. * +1 Important filesystem/storage path. The flaw is in EROFS decompression global-buffer management, a filesystem data path that may be exercised during normal file access. * +1 Weak exploitation concern. This is more than a NULL dereference or passive warning because the primitive is a real heap OOB write involving kernel page pointer arrays, but payload and target control are not established. Non-awarded signals: * Strong CLASS_A corruption was not awarded because the overflow payload appears to be existing kernel page pointers, and attacker control over target object or replacement contents is not established. * Controlled reclaim, arbitrary write, callback control, credential overwrite, or demonstrated LPE are not established. * Confidentiality and integrity bonuses were not awarded because there is no demonstrated leak, protected object overwrite, or controlled security-state modification. * Remote reachability was not awarded. This is a filesystem/local path, not a network-triggered path. * RealUAF was not awarded. The patch establishes an OOB write, not use-after-free. * Extra availability was not awarded because the crash/corruption DoS is already counted once. * Concrete repeated release/refcount was not awarded. No first put/free followed by a second lifetime mutation on the same dangling reference is shown. 3. Reachability analysis The vulnerable path is local and tied to EROFS compressed-data handling and global buffer resizing. An ordinary local user may be able to exercise the runtime decompression path by reading files from an already mounted EROFS filesystem, but the supplied evidence does not fully establish whether an attacker can provide the filesystem image or force the required resize sequence without prior host-admin setup. HostAdminRequired is therefore UNKNOWN. If exploitation requires mounting a crafted EROFS image, that may require host administrator privilege in many deployments. If the vulnerable filesystem is already mounted and attacker-controlled file access can trigger the resize retry sequence, below-host-admin reachability may be possible. NamespaceScopedPrivilege is NO because no namespace-scoped capability path is relevant or established. There is no direct network trigger. No special hardware is required. The condition is not described as a timing race, but it does require a partial resize failure followed by a retry with an intermediate size, so practical triggering depends on memory pressure and filesystem/workload behavior. 4. Primitive and severity interpretation The exact primitive is a heap out-of-bounds write caused by allocating tmp_pages for the requested nrpages while copying existing entries based on a larger already grown gbuf->nrpages value. This is not fixed stale storage and not a UAF. It is a kernel heap corruption candidate affecting an array of page pointers. The demonstrated consequence is at least local denial of service through kernel memory corruption and probable crash. The speculative consequence is stronger exploitation through corruption of adjacent heap objects, but the patch does not establish controlled target selection, controlled payload contents, controlled reclaim, or a concrete privilege escalation path. PrimitiveClass is CLASS_B because a real kernel corruption primitive exists and needs exploitation-leverage review, but the currently supplied evidence does not establish a strong CLASS_A primitive. ImportantCandidate is YES because heap OOB writes in kernel filesystem code should not be automatically downgraded when exploitation leverage remains unresolved. AutoDowngradeAllowed is NO because automatic closure would lose a concrete memory-corruption primitive that requires manual assessment. Likely operational severity is actionable Moderate at minimum, with possible Important consideration depending on whether below-host-admin triggering and useful heap corruption control can be demonstrated. 5. One-sentence report phrase An EROFS global buffer resize retry can allocate a temporary page pointer array that is smaller than the already grown buffer and then copy too many existing pointers into it, causing a local kernel heap out-of-bounds write and potential DoS or stronger memory-corruption impact. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch establishes a concrete kernel heap out-of-bounds write involving page pointer arrays, and the practical attacker reachability and exploitation leverage beyond crash remain unresolved. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: erofs: skip sufficiently large global buffers when resizing [ Upstream Commit: 7267557ce98ccd07faaf3bc86382448950cc4ff6 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7267557ce98ccd07faaf3bc86382448950cc4ff6 Changed files: fs/erofs/zutil.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=7267557ce98ccd07faaf3bc86382448950cc4ff6 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89602 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89602 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:L/I:L/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: unknown 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).