From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-45951][IMPORTANT] bpf: Fix a potential use-after-free of BTF object [ Upstream Date: Wed, 27 May 2026 19:46:37 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-45951 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 8 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: eac65c272f3b49021a843cba5107d63627395e0e List-Id: CVE: CVE-2026-45951 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: bpf: Fix a potential use-after-free of BTF object [ Upstream Commit: eac65c272f3b49021a843cba5107d63627395e0e Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=eac65c272f3b49021a843cba5107d63627395e0e Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45951 Analysis date: Wed, 27 May 2026 19:46:37 -0400 ActionableScore: 8 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45951 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45951 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: IMPORTANT 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-2026-45951 IMPORTANT CHECK 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-416;CWE-911;*CWE-664;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'BPF verifier refcounting for BTF objects was inconsistent and could pass a zero refcounted BTF object into pseudo BTF ID checking or used BTF tracking. A local user with access to BPF program loading and BTF FDs can exercise this verifier path and trigger a use after free of a BTF object. For the CVSS the PR:L is used because BPF access may be delegated through CAP_BPF, CAP_SYS_ADMIN, or system policy, and does not always imply full host root. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to memory corruption in a high control BPF verifier path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) MAYBE OOB BPF LEAK UAF LINUS SYZBOT KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=6 1. ActionableScore * Conservative score: 6 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: 2. Signal breakdown * Local trigger: +1. A local user with access to BPF program loading and BTF FDs can reach the verifier path. * Local high-control kernel API: +1. BPF verifier input is highly user-controlled and historically security-sensitive. * Generic memory corruption, strong primitive: +2. The patch fixes a potential use-after-free of a BTF object. * Real lifetime corruption: +1. The root cause is incorrect BTF refcount ownership and use of zero-refcounted objects. * Reliable kernel crash / strong DoS: +1. A UAF of verifier-owned BTF state can crash the kernel. * Paranoid LPE plausibility: +2. UAF in the BPF verifier is a high-risk class because attacker-controlled verifier inputs may influence object lifetime, layout, and reuse, even though this patch does not show a complete exploit chain. * Hard/specific path: -1. Exploitation depends on specific pseudo BTF ID or FD-array verifier paths and refcount timing. * No network reachability. This is local only. 3. Reachability analysis The issue is reachable through local BPF program verification paths that use BTF objects or BTF FDs. Access may require `CAP_BPF`, `CAP_SYS_ADMIN`, or permissive system policy, but this is still PR:L rather than full host-root in many delegated environments. Containers matter if they are granted BPF capabilities or BPF program loading access. There is no remote network trigger. 4. Severity interpretation This is an Important-class candidate in paranoid triage. The bug is a real BTF object lifetime/refcounting problem in the BPF verifier, not a resource leak or warning. Conservative impact is Actionable Moderate because a practical LPE primitive is not demonstrated. Paranoid impact is high because UAF in BPF verifier code is a historically dangerous bug class. 5. One-sentence report phrase Incorrect BTF refcount handling in the BPF verifier can pass a zero-refcounted BTF object into pseudo-BTF-ID validation or used-BTF tracking, creating a local verifier UAF. 6. Manual review recommendation MANUAL CHECK REQUIRED. This is a local high-control BPF verifier UAF, and BPF verifier lifetime bugs should not be auto-closed as DoS-only even without a published exploit. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Fix a potential use-after-free of BTF object [ Upstream Commit: eac65c272f3b49021a843cba5107d63627395e0e Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=eac65c272f3b49021a843cba5107d63627395e0e Changed files: kernel/bpf/verifier.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=eac65c272f3b49021a843cba5107d63627395e0e ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45951 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45951 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: 6 Paranoid ActionableScore: 8 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: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT 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).