From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-93045][MODERATE 7.0] bpf: Reject arena frees below the arena base [ Upstream Date: Fri, 18 Sep 2026 09:29:25 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-93045 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: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 90453eaf8f14e7be0ab03983f2a93aeb6b990a58 List-Id: CVE: CVE-2026-93045 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: bpf: Reject arena frees below the arena base [ Upstream Commit: 90453eaf8f14e7be0ab03983f2a93aeb6b990a58 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=90453eaf8f14e7be0ab03983f2a93aeb6b990a58 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93045 Analysis date: Fri, 18 Sep 2026 09:29:25 -0400 ActionableScore: 6 ActionableScore lower bound: 5 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-2026-93045 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93045 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-2026-93045 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-93045 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:H/I:H/A:H';CWE-763;CWE-191;*CWE-787;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'bpf_arena_free_pages accepts scalar arena addresses and reconstructs a full user address from the arena base after masking to the low 32 bits. If the scalar value is below the low 32 bits of arena user_vm_start, full_uaddr can fall below the arena mapping and the free tree can receive an out-of-range offset. A later arena allocation may reuse that offset and return an address below the expected arena range, which makes this a memory safety issue rather than a pure warning or resource leak. For the CVSS the PR:L is used because a local process with access to BPF arena operations or delegated BPF capabilities can reach the path, while the issue is not network reachable. Impact is at least local denial of service and may include confidentiality or integrity impact if the out-of-range arena address can be used as a practical memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) YES OOB BPF SIMPLEFIX LINUS KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 PrimitiveClass=CLASS_B RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 4 * Conservative score: 5 * Applied conservative floor/cap: 4 -> 5 because the patch establishes attacker-influenced allocator/free-tree state corruption that can later return an out-of-range arena address, so automatic closure below actionable Moderate is unsafe. * Raw paranoid score: 6 * Paranoid score: 6 * Applied paranoid floor/cap: none. The BPF privileged-control-plane cap does not reduce below 6. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Positive signals: * +2: Concrete Class B memory-safety primitive. A scalar free below the low 32 bits of the arena base can produce full_uaddr below user_vm_start, causing an out-of-range free-tree offset. * +1: Practical primitive chain is directly described. A later allocation can reuse the corrupted offset and return an address below the arena mapping. * +1: Memory layout and range invariant restoration. The patch restores the invariant that a reconstructed arena user address must not fall below arena->user_vm_start before free-range clipping. * +1 paranoid only: Stronger unresolved exploitation leverage. The same BPF arena mechanism can place an invalid range into allocator state and later consume it as an allocation result, which is more than a warning or crash-only check. * +1 paranoid only: Attacker-influenced allocator operation. The scalar address and later allocation behavior are plausibly controlled by the actor that can exercise BPF arena operations. Negative signals: * -1 conservative: BPF arena access is privilege-gated in normal deployments. Complete below-host-admin reachability is not established from the supplied patch. Important non-awarded signals: * RealUAF not awarded because this is not a use-after-free or stale post-lifetime object use. * Concrete repeated release/refcount not awarded because no first release, surviving exact reference, and second lifetime mutation are established. * Controlled reclaim not demonstrated. * Arbitrary kernel read/write not demonstrated. * Direct LPE not demonstrated. * Remote reachability not established. * Reliable kernel crash not separately awarded because the patch describes out-of-range allocation behavior, not a demonstrated panic path. * Confidentiality and integrity bonuses are not separately awarded because the patch does not establish a concrete disclosure path or unauthorized write to protected state. * Class A not assigned because the patch establishes a dangerous allocator/range corruption primitive, but not controlled arbitrary write, controlled reclaim, callback control, credential modification, or demonstrated LPE. Repeated-release/refcount checklist: * First release can end lifetime: not applicable. * Exact same reference survives: not applicable. * Second operation mutates lifetime/refcount: not applicable. * +1 Concrete repeated release/refcount awarded: no. * Paranoid repeated-refcount leverage awarded: no. * FLOOR 5 applied: yes, but due to unresolved allocator memory-safety primitive, not repeated release. 3. Reachability analysis The vulnerable path is in BPF arena page freeing. The actor must be able to create and use BPF arena functionality and pass scalar arena addresses that reach bpf_arena_free_pages. Ordinary unprivileged reachability is not established. Modern BPF usage is commonly gated by CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, LSM policy, sysctl settings, or product-specific delegation. The supplied evidence does not prove that the complete load, map creation, arena operation, and trigger sequence is available to an ordinary local user. HostAdminRequired is UNKNOWN rather than YES because the patch does not positively establish that host-root-equivalent privilege is mandatory in all relevant deployments. HostAdminRequired is not NO because below-host-admin reachability is also not proven. NamespaceScopedPrivilege is UNKNOWN. The input does not show that all required BPF arena operations are available with attacker-created namespace-scoped capabilities. No network trigger is established. No special hardware dependency is established. No race or narrow timing requirement is established. The bug appears to be an ordered invalid-free and later-allocation sequence rather than a timing race. 4. Primitive and severity interpretation The exact primitive is an attacker-influenced invalid arena free below the arena base. The low 32 bit address reconstruction can produce a full user address below user_vm_start. The old clipping logic can then create an out-of-range free-tree offset, and later allocation can return an address below the arena mapping. This is an active allocator/range-state corruption issue, not a fixed stale-buffer crash and not a cleanup-only destructor issue. It is also not a Real UAF. PrimitiveClass is CLASS_B because a real potentially exploitable memory-safety primitive exists, but the supplied evidence does not establish Class A strength such as arbitrary kernel read/write, controlled reclaim, credential overwrite, callback control, or demonstrated privilege escalation. The demonstrated consequence is invalid allocator state and out-of-range allocation. The speculative consequence is that the out-of-range arena address may become a practical memory corruption or privilege-escalation primitive depending on how the returned address is consumed by BPF arena users. ImportantCandidate is YES because this is a BPF memory-safety primitive with unresolved exploitation leverage beyond simple DoS. AutoDowngradeAllowed is NO because automatic downgrade would discard a concrete allocator corruption primitive that requires manual security review. Likely operational severity is actionable Moderate at minimum, with Strong Important candidacy depending on whether manual analysis confirms that the below-arena returned address can be used for meaningful kernel memory corruption or privilege escalation. 5. One-sentence report phrase A BPF arena invalid free below the arena base can corrupt the arena free tree so that a later allocation returns an address below the arena mapping, making this an actionable memory-safety issue that requires manual review. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch establishes a concrete out-of-range allocator state primitive in BPF arena code, and the practical impact depends on whether the returned below-arena address can be converted into useful memory corruption or privilege escalation. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Reject arena frees below the arena base [ Upstream Commit: 90453eaf8f14e7be0ab03983f2a93aeb6b990a58 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=90453eaf8f14e7be0ab03983f2a93aeb6b990a58 Changed files: kernel/bpf/arena.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=90453eaf8f14e7be0ab03983f2a93aeb6b990a58 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-93045 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93045 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:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.8 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: 5 Paranoid ActionableScore: 6 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).