From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74337][MODERATE REGULAR] bpf: Fix NMI/tracepoint re-entry deadlock on lru locks [ Upstream Date: Sat, 15 Aug 2026 12:36:37 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74337 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: 3 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: 8b0510cc3a4a000d4ed1a56cd96231f3d3ba94c5 List-Id: CVE: CVE-2026-74337 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: bpf: Fix NMI/tracepoint re-entry deadlock on lru locks [ Upstream Commit: 8b0510cc3a4a000d4ed1a56cd96231f3d3ba94c5 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8b0510cc3a4a000d4ed1a56cd96231f3d3ba94c5 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74337 Analysis date: Sat, 15 Aug 2026 12:36:37 -0400 ActionableScore: 3 ActionableScore lower bound: 1 Actionable bucket: Borderline manual review recommended. Not an Important candidate Manual review required: YES Summary: A BPF LRU lock re-entry bug can allow NMI or tracepoint BPF execution to recursively acquire per-CPU or global LRU locks on the same CPU, causing a local denial of service through AA-deadlock or recursive locking. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74337 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74337 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-2026-74337 MODERATE 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:N/I:N/A:H';CWE-667;*CWE-833;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'BPF LRU map operations can deadlock when an NMI/tracepoint BPF program re-enters the same per-CPU or global LRU lock already held on the same CPU. This can produce recursive locking or AA-deadlock conditions and lead to a local denial of service by stalling CPU progress. For the CVSS the PR:L is used for the paranoid score because delegated BPF or tracing capabilities may be available to non root service accounts or constrained administrative contexts, although typical production systems require stronger privileges to load such programs. The issue is not network reachable and is triggered through local BPF execution paths rather than packet traffic. Impact is denial of service only, with no supported evidence of information disclosure or privilege escalation from the shown locking bug.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended. Not an Important candidate (with actual score 2) YES LOCK DEADLOCK INIT BPF LEAK HARDWARE LINUS SYZBOT INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 3 * Final recommended bucket: **Borderline manual review recommended. Not an Important candidate**:: ## 2. Signal breakdown Conservative signals: * Reliable kernel crash / strong DoS: +1. The bug can create an AA-deadlock or recursive locking condition on BPF LRU locks, causing CPU soft lockups or stalled kernel progress. * Requires admin/root/CAP_* in typical deployments: -2. Loading and attaching NMI or tracepoint BPF programs typically requires CAP_BPF, CAP_PERFMON, CAP_SYS_ADMIN, or root-controlled BPF policy. * Broad/default/common subsystem: +1. BPF is a broadly deployed kernel subsystem, although this specific path requires privileged BPF use. Paranoid signals: * Reliable kernel crash / strong DoS: +1. * Availability impact realistic: +1. The deadlock can stall CPU progress and may become system-visible through watchdog soft lockups. * Broad/default/common subsystem: +1. * No memory corruption signal is awarded. The patch fixes lock re-entry and recovery windows, but does not show UAF, OOB write, type confusion, attacker-controlled reclaim, or arbitrary write. * No LPE signal is awarded. The issue is DoS-only based on the shown patch and commit context. ## 3. Reachability analysis The trigger requires local BPF execution through NMI or tracepoint BPF programs that can re-enter BPF LRU map allocation or free paths on the same CPU. In typical hardened product configurations, unprivileged BPF is disabled and this requires privileged capabilities, so the conservative score is low. In a paranoid deployment model, delegated tracing or BPF permissions may be available to service accounts, container root, or constrained administrators, so the privilege penalty is reduced. The issue is not network reachable and is not triggered by packet traffic alone. Call-site confidence: high, because the patch shows the affected LRU pop, push, steal, local-list, and recovery paths. ## 4. Severity interpretation This behaves like a local privileged or delegated-capability denial-of-service issue, not an Important-class memory corruption vulnerability. The theoretical risk is limited to deadlock and node recovery correctness. The realistic evidence supports CPU lockup or kernel availability impact, but does not support confidentiality impact, integrity impact, or privilege escalation. ## 5. One-sentence report phrase A BPF LRU lock re-entry bug can allow NMI or tracepoint BPF execution to recursively acquire per-CPU or global LRU locks on the same CPU, causing a local denial of service through AA-deadlock or recursive locking. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a BPF re-entry locking bug with syzbot reports and non-trivial recovery paths, so it should not be auto-closed solely as a low CVSS DoS, but current evidence does not justify Important severity. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Fix NMI/tracepoint re-entry deadlock on lru locks [ Upstream Commit: 8b0510cc3a4a000d4ed1a56cd96231f3d3ba94c5 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8b0510cc3a4a000d4ed1a56cd96231f3d3ba94c5 Changed files: kernel/bpf/bpf_lru_list.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=8b0510cc3a4a000d4ed1a56cd96231f3d3ba94c5 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74337 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74337 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:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H 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: 1 Paranoid ActionableScore: 3 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).