From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53081][IMPORTANT] bpf: Enforce regsafe base id consistency for BPF_ADD_CONST scalars [ Upstream Date: Wed, 24 Jun 2026 13:30:53 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53081 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: 5 X-AL-KERNEL-Commit: 13c02881e49aac4c82b261faa26db9edf2567231 List-Id: CVE: CVE-2026-53081 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: bpf: Enforce regsafe base id consistency for BPF_ADD_CONST scalars [ Upstream Commit: 13c02881e49aac4c82b261faa26db9edf2567231 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=13c02881e49aac4c82b261faa26db9edf2567231 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53081 Analysis date: Wed, 24 Jun 2026 13:30:53 -0400 ActionableScore: 8 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A BPF verifier state-pruning flaw in BPF_ADD_CONST scalar ID handling can allow inconsistent base register relationships to be treated as safe, potentially enabling a crafted local eBPF program to bypass verifier assumptions and reach kernel memory safety violations. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53081 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53081 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-2026-53081 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-20;CWE-682;*CWE-787;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7';DESCR 'A BPF verifier logic flaw can let regsafe treat two scalar states as compatible even when their BPF_ADD_CONST compound ids derive from different base ids. This can make verifier state pruning accept an unsafe state relation and may allow a crafted eBPF program to pass verification with incorrect assumptions about linked registers and scalar bounds. For the CVSS the PR:L is used for the paranoid score because BPF program loading can be available to non full admin local users in delegated CAP_BPF service container or older unprivileged BPF configurations. The issue is local and is not network reachable by itself. Impact may include confidentiality integrity and availability compromise because verifier bypass bugs can lead to unsafe kernel memory access and possible local privilege escalation. Exploitation complexity is high because the attacker must craft verifier states that trigger the inconsistent id mapping and pruning behavior.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES BPF KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Privilege escalation plausible: +2. BPF verifier soundness bugs can allow an unsafe eBPF program to pass verification and later access kernel memory incorrectly. * Memory corruption, weak/indirect corruption candidate: +1. The patch shows incorrect verifier state equivalence and unsafe pruning, but does not directly show a concrete OOB write or arbitrary write primitive. * Local unprivileged high-control kernel data-plane API: +1. BPF is a high-control kernel API where users can shape verifier states and register relationships. * Confidentiality impact plausible: +1. Unsafe verifier assumptions can plausibly lead to kernel memory disclosure. * Integrity impact plausible: +1. Unsafe verifier assumptions can plausibly lead to kernel memory corruption. * Availability impact realistic: +1. A malformed accepted BPF program can plausibly crash the kernel. * Broad/default/common subsystem: +1. BPF is widely deployed and security-sensitive. * Hard or unreliable construction: -1. Triggering requires a crafted verifier state involving BPF_ADD_CONST scalar ID relationships and state pruning. * Requires CAP_BPF/CAP_SYS_ADMIN in typical deployments: -2. On many production systems, BPF program loading is restricted. Conservative total: 5. Paranoid additions/changes: * Local low-privilege trigger: +1. In some environments BPF loading is delegated to non-full-admin users, services, containers, or older unprivileged BPF configurations. * Do not apply full admin penalty in paranoid mode. CAP_BPF or delegated BPF access is not equivalent to full host root if verifier bypass crosses into arbitrary kernel memory access. Paranoid total: 8. ## 3. Reachability analysis The bug is locally reachable through BPF program loading and verifier state pruning. It is not network-triggerable by itself. In typical hardened deployments, loading relevant BPF programs requires CAP_BPF, CAP_SYS_ADMIN, or equivalent privileges, which supports the conservative score. However, BPF access is sometimes delegated to service accounts, containerized workloads, observability agents, or restricted root contexts, and older systems may expose unprivileged BPF depending on configuration. In those cases the effective attacker privilege can be closer to PR:L than PR:H. Realistic exploitation is non-trivial because the attacker must construct verifier states where BPF_ADD_CONST compound IDs are accepted while their stripped base IDs are inconsistent. But verifier pruning bugs are historically high-risk because a single unsound equivalence can invalidate later memory safety reasoning. ## 4. Severity interpretation This is not an ordinary DoS-only bug. It is a BPF verifier logic flaw that can cause unsafe state pruning, which is a known high-risk class because it may allow a crafted eBPF program to pass verification under incorrect register and scalar-bound assumptions. The realistic evidence from the patch supports at least Actionable Moderate handling. The paranoid interpretation supports a Strong Important candidate because verifier bypass bugs can plausibly lead to kernel memory disclosure, memory corruption, and local privilege escalation, even though the patch itself does not demonstrate a final arbitrary write primitive. ## 5. One-sentence report phrase A BPF verifier state-pruning flaw in BPF_ADD_CONST scalar ID handling can allow inconsistent base register relationships to be treated as safe, potentially enabling a crafted local eBPF program to bypass verifier assumptions and reach kernel memory safety violations. ## 6. Manual review recommendation MANUAL CHECK REQUIRED. This is a verifier soundness issue in a high-risk subsystem with plausible LPE impact, and the final exploitability depends on whether a concrete unsafe memory access program can be constructed and on the target system BPF privilege model. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Enforce regsafe base id consistency for BPF_ADD_CONST scalars [ Upstream Commit: 13c02881e49aac4c82b261faa26db9edf2567231 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=13c02881e49aac4c82b261faa26db9edf2567231 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=13c02881e49aac4c82b261faa26db9edf2567231 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53081 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53081 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:H/I:H/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: 5 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).