From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-92520][MODERATE REGULAR] bpf: Zero queue and stack outputs on lock failure [ Upstream Date: Fri, 18 Sep 2026 03:39:54 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-92520 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 1534c4bff3aaca19c4c9a82f93e9b81f7c983de3 List-Id: CVE: CVE-2026-92520 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: bpf: Zero queue and stack outputs on lock failure [ Upstream Commit: 1534c4bff3aaca19c4c9a82f93e9b81f7c983de3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1534c4bff3aaca19c4c9a82f93e9b81f7c983de3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92520 Analysis date: Fri, 18 Sep 2026 03:39:54 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-92520 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92520 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 REGULAR 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-2026-92520 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-92520 CHECK WITH IMPACT FROM ORIG NN LOW 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:N/A:N';*CWE-457;CWE-908;*CWE-200;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.7';DESCR 'BPF queue and stack map pop or peek helpers can return -EBUSY after a failed raw_res_spin_lock_irqsave without initializing the output value buffer. The verifier treats this helper output as initialized, so a BPF program may observe stale stack bytes after the failed call. For the CVSS the PR:L is used in the paranoid score because some deployments may allow a local user or a limited service account with CAP_BPF or similar rights to load or run the affected BPF program. The issue is not network reachable. Impact is primarily confidentiality exposure of kernel or BPF stack contents, and it may help bypass mitigations or support later attacks, but the patch does not show a write primitive or direct privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES LOCK DEADLOCK BPF SIMPLEFIX ERRORPATH LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 3 * Conservative score: 3 * Raw paranoid score: 4 * Paranoid score: 4 * Final recommended bucket: **Borderline / manual review recommended**:: No UAF floor applies. No BPF cap changes the score because the raw score is already below the BPF privileged control-plane cap. 2. Signal breakdown Conservative positive signals: * +1 Confidentiality plausible: the helper can return -EBUSY without initializing the output buffer, and the commit explicitly states that BPF programs can observe uninitialized stack contents. * +1 User-observable disclosure path: the verifier treats the helper output as initialized, so the BPF program can legally consume bytes that were not actually written by the helper. * +1 Security-relevant verifier/helper contract violation: the helper breaks the expected initialization guarantee relied on by verifier safety reasoning. Paranoid additional signal: * +1 Repeated disclosure concern: if an attacker has practical BPF execution rights and can repeatedly hit the lock-failure path, the issue may disclose more than a single trivial value and may aid mitigation bypass or later exploit development. Non-awarded signals: * UAF not awarded: no freed object or stale lifetime use is established. * Memory corruption not awarded: the patch shows missing memset on an error path, not a write primitive or object corruption. * Controlled reclaim not demonstrated. * Arbitrary read or arbitrary write not demonstrated. * Privilege escalation not demonstrated. * Reliable crash or DoS not awarded: the demonstrated effect is information exposure, not kernel panic. * Remote reachability not established. * Local unprivileged trigger not awarded because complete below-host-admin BPF reachability is not established. * Strong Class A kernel disclosure not awarded because the leak is gated by BPF execution and failed lock acquisition, and the amount and sensitivity of leaked data are not fully established. * BPF high-control API bonus not awarded because ordinary unprivileged access to the complete trigger path is not proven. * No negative host-admin penalty applied because host-admin-equivalent privilege is not positively established. Concrete repeated release/refcount checklist: * First release can end lifetime: no. * Exact same reference survives: no. * Second lifetime/refcount mutation exists: no. * Concrete repeated release/refcount +1 awarded: no. * Paranoid repeated-refcount leverage +1 awarded: no. * FLOOR 5 applied: no. 3. Reachability analysis The trigger requires execution of a BPF program that uses queue or stack map pop or peek helpers and reaches the failed raw_res_spin_lock_irqsave path. BPF program loading is commonly restricted by CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN for some program types, or by root-controlled sysctls such as unprivileged_bpf_disabled. The supplied patch does not prove that an ordinary local user can load and run the required program in the evaluated environment. HostAdminRequired is UNKNOWN because the complete privilege boundary is not resolved from the supplied input. It is also not safe to mark HostAdminRequired=YES, because BPF rights may be delegated to non-root service accounts or enabled in some environments. NamespaceScopedPrivilege is UNKNOWN. Some BPF or netdevice-related operations can be namespace-sensitive, but the supplied evidence does not establish that the full load, map creation, helper execution, and observation chain is available through attacker-created namespaces. No network trigger is present. No prior special hardware requirement is indicated. The failed lock acquisition may require contention or NMI-like circumstances, but the evidence is insufficient to score a hard timing penalty. 4. Primitive and severity interpretation The exact primitive is a constrained kernel information disclosure through uninitialized helper output. The verifier assumes the helper initializes the output buffer, but the -EBUSY path did not write to it. As a result, a BPF program may read stale stack bytes that should have been zeroed. This is not an active structured-object UAF, not fixed stale storage, and not a repeated refcount/lifetime mutation. The demonstrated consequence is confidentiality exposure. The speculative consequence is that leaked stack bytes may assist later exploitation or mitigation bypass, but the patch does not establish arbitrary read, arbitrary write, controlled corruption, callback control, or direct LPE. PrimitiveClass is NONE because no kernel corruption, lifetime, ownership, authorization, COW, or similar stronger primitive is established by the patch. ImportantCandidate is NO because the evidence supports a BPF-gated info leak rather than an Important-grade corruption or boundary-bypass primitive. AutoDowngradeAllowed is YES because no unresolved Class A or Class B exploitation leverage remains, although manual review is still recommended due to the kernel stack disclosure angle. Likely operational severity is Borderline Moderate. It should not be treated as a crash-only bug, but it also should not be escalated to Important without stronger evidence of unprivileged BPF reachability, substantial disclosure, or an exploit chain. 5. One-sentence report phrase BPF queue and stack map helpers may return -EBUSY without clearing the verifier-trusted output buffer, allowing a BPF program with suitable execution rights to observe uninitialized stack contents and potentially leak kernel information. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: this is a kernel information leak candidate through BPF helper semantics, but no UAF, write primitive, direct LPE, or proven unprivileged reachability is established. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Zero queue and stack outputs on lock failure [ Upstream Commit: 1534c4bff3aaca19c4c9a82f93e9b81f7c983de3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1534c4bff3aaca19c4c9a82f93e9b81f7c983de3 Changed files: kernel/bpf/queue_stack_maps.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=1534c4bff3aaca19c4c9a82f93e9b81f7c983de3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-92520 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92520 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:H/UI:N/S:U/C:L/I:N/A:N The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N The Best / paranoid CVSS score: 4.7 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: 3 Paranoid ActionableScore: 4 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 REGULAR 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).