From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53090][IMPORTANT] bpf: Fix ld_{abs,ind} failure path analysis in subprogs [ Upstream Date: Fri, 26 Jun 2026 13:31:53 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53090 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: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: d846d83bdacbd8f14fc45c63b8c1d22608452e1c List-Id: CVE: CVE-2026-53090 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: bpf: Fix ld_{abs,ind} failure path analysis in subprogs [ Upstream Commit: d846d83bdacbd8f14fc45c63b8c1d22608452e1c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d846d83bdacbd8f14fc45c63b8c1d22608452e1c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53090 Analysis date: Fri, 26 Jun 2026 13:31:53 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A BPF verifier path-analysis bug allowed ld_abs and ld_ind subprogram failure exits to be missed, potentially creating a verified-state versus runtime-state mismatch that warrants manual review for local privilege escalation risk. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53090 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53090 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-2026-53090 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-754;*CWE-20;CWE-755;CWE-670;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'Manual review is recommended because this is a BPF verifier soundness issue rather than a simple crash bug. I cannot perform live Internet search from here, so the assessment is based on the provided patch text and general Linux BPF verifier behavior.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) MAYBE INIT BPF SKB PACKET KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative scoring: * Local unprivileged trigger: +1 A local process that can load BPF programs can reach the verifier path. * Weak LPE concern: +1 This is a BPF verifier soundness bug where runtime behavior may differ from verified behavior. * Memory corruption, Weak/indirect corruption candidate: +1 The patch does not show a direct arbitrary write or UAF, but verifier state mismatch can be a precursor to unsafe kernel memory access. * Local unprivileged high-control kernel data-plane API: +1 BPF is a high-control kernel API with user-shaped programs and verifier state. * Broad/common subsystem exposure: +1 The BPF verifier is a core kernel security boundary used across many deployments. * Hard or unreliable construction: -1 Triggering requires a crafted BPF subprogram using ld_abs or ld_ind, BTF annotated scalar return constraints, and the abnormal load-failure path. Paranoid additions: * Strong LPE plausibility: +2 instead of weak +1 BPF verifier unsoundness historically has strong local privilege escalation relevance even when the primitive is not fully demonstrated in the patch. * Confidentiality impact plausible: +1 If verifier unsoundness is converted into unsafe memory access, kernel data exposure is plausible. * Integrity impact plausible: +1 If verifier unsoundness is converted into unsafe memory access, kernel memory modification or privilege escalation is plausible. ## 3. Reachability analysis The bug is local, not network reachable by itself. It requires the ability to load a BPF program that reaches ld_abs or ld_ind inside a subprogram and relies on the verifier missing the hidden abnormal return path emitted by bpf_gen_ld_abs. Privileges depend heavily on deployment. On hardened systems, unprivileged BPF is often disabled and loading such programs may require CAP_BPF, CAP_SYS_ADMIN, or related privileges. In less restricted configurations, or in environments where BPF access is delegated to services or containers, this can be closer to a local low-privilege attack surface. Namespaces do not automatically make this safe, because delegated BPF capability or service-level access can still expose the verifier boundary. Realistic exploitation is non-trivial because it requires a carefully constructed verifier/runtime state mismatch, but the affected component is security-sensitive. ## 4. Severity interpretation This should not be treated as an ordinary Moderate auto-close issue. The patch fixes verifier path analysis, not a simple crash or resource leak. The immediate evidence is a verifier logic flaw with no direct demonstrated arbitrary write in the diff, so the conservative score is Actionable Moderate. The paranoid score is Strong Important candidate because BPF verifier unsoundness can plausibly become a local privilege escalation primitive if the unverified abnormal return state enables unsafe assumptions in caller state. Theoretical memory corruption potential is stronger than for ordinary DoS bugs, but the patch alone does not prove a reliable exploit primitive. ## 5. One-sentence report phrase A BPF verifier path-analysis bug allowed ld_abs and ld_ind subprogram failure exits to be missed, potentially creating a verified-state versus runtime-state mismatch that warrants manual review for local privilege escalation risk. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a BPF verifier soundness issue in a high-control local kernel API. Even without a demonstrated exploit primitive in the patch, this class has enough LPE relevance that it should not be auto-closed. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Fix ld_{abs,ind} failure path analysis in subprogs [ Upstream Commit: d846d83bdacbd8f14fc45c63b8c1d22608452e1c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d846d83bdacbd8f14fc45c63b8c1d22608452e1c 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=d846d83bdacbd8f14fc45c63b8c1d22608452e1c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53090 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53090 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: 5 Paranoid ActionableScore: 7 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).