From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98063][MODERATE REGULAR] bpf: Fix NULL-ptr-deref in btf_var_show() [ Upstream Date: Mon, 28 Sep 2026 20:17:43 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98063 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: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: e472ae0d97865e2021ee668a13eab64013aebf23 List-Id: CVE: CVE-2026-98063 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: bpf: Fix NULL-ptr-deref in btf_var_show() [ Upstream Commit: e472ae0d97865e2021ee668a13eab64013aebf23 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e472ae0d97865e2021ee668a13eab64013aebf23 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98063 Analysis date: Mon, 28 Sep 2026 20:17:43 -0400 ActionableScore: 1 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98063 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98063 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98063 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98063 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in btf_var_show occurs because btf_type_id_resolve accesses btf resolved_ids even when it is NULL for a base BTF such as the vmlinux BTF used by bpf_snprintf_btf. A local BPF program can trigger the issue by passing the type ID of a BTF_KIND_VAR from the vmlinux BTF and invoking the affected formatting path. For the CVSS the PR:L value is used because the attacker must be able to load or execute a suitable BPF program through the local BPF interface, while this access may be delegated through limited capabilities and does not always imply full system administration. The issue is not network reachable. The demonstrated primitive is an invalid read through a NULL pointer rather than a UAF, OOB write, or arbitrary write. Impact is a local denial of service through a kernel Oops and may become a full kernel panic when panic_on_oops or an equivalent policy is enabled.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE KASAN NULLPTR BPF LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 1 * Paranoid score: 1 * No floor or cap changed either score. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable kernel fault / DoS. Passing a vmlinux BTF_KIND_VAR to `bpf_snprintf_btf()` reaches `btf_var_show()`, where `btf_type_id_resolve()` dereferences the NULL `btf->resolved_ids` pointer. The supplied trace confirms the fault. * +0 Weak corruption concern. The primitive is a low-address invalid read through a NULL-derived pointer. No write, stale lifetime operation, disclosure path, or independently useful corruption primitive is established. * +0 Local unprivileged trigger. Not awarded because the complete BPF program load and execution path is not established as available to an ordinary user. * +0 Strong or weak LPE leverage. No controlled reclaim, object replacement, type confusion, arbitrary write, callback influence, or credential effect is shown. * +0 Extra Availability. Not awarded because panic under `panic_on_oops` is the stronger manifestation of the same NULL dereference, not a distinct availability mechanism. * +0 Confidentiality and Integrity. The internal invalid read is not shown to disclose data or modify kernel state. * +0 Remote reachability. The path is reached through the local BPF syscall interface, not network traffic. * No privilege penalty was applied because host-admin-equivalent privilege is not positively established. * No race, rare-hardware, subsystem-rarity, or configuration penalty was applied. * Repeated release/refcount analysis is not applicable. There is no release, surviving dangling reference, second lifetime mutation, or UAF. * REAL UAF FLOOR 4 and FLOOR 5 do not apply. * The BPF control-plane cap does not change the score because it is a maximum rather than a target. 3. Reachability analysis The demonstrated trigger is a local BPF program invoking `bpf_snprintf_btf()` with a `BTF_KIND_VAR` type ID from base vmlinux BTF. The supplied trace reaches the path through `bpf_prog_test_run_raw_tp()` and `__sys_bpf()`. The complete privilege boundary is unresolved. Loading and executing the relevant BPF program may require `CAP_BPF`, `CAP_SYS_ADMIN`, another capability combination, or access granted by a privileged BPF service, depending on kernel and product policy. The input does not establish that an ordinary user can complete this sequence, but it also does not prove that full host-admin-equivalent control is required. Therefore `HostAdminRequired=UNKNOWN`. No attach or netdevice stage is demonstrated, and no evidence establishes that all required operations work inside an attacker-created user or network namespace. Therefore `NamespaceScopedPrivilege=UNKNOWN`. No network trigger, prior device setup, special hardware, timing race, or repeatability constraint is involved. Once suitable BPF execution access exists, the invalid type presentation appears deterministic. 4. Primitive and severity interpretation The exact primitive is an invalid read through a NULL-derived `btf->resolved_ids` address. It is neither active structured-object UAF nor fixed stale storage because no object lifetime has ended. There is no cleanup-only stale use and no repeated release or refcount mutation. This is `CLASS_C`: the demonstrated behavior is a NULL pointer dereference leading to an Oops and potentially a host panic under fatal-Oops policy. The patch-supported practical consequence is local denial of service. Privilege escalation, disclosure, and write-based corruption are unsupported theoretical consequences and are not scored. `ImportantCandidate=NO` because no Class A primitive or meaningful unresolved Class B lifetime/corruption leverage exists. `AutoDowngradeAllowed=YES` because the root cause and terminal behavior are constrained to invalid-read/crash behavior, with no unresolved ownership, authorization, lifetime, or security-boundary primitive. Likely operational severity is Low-like to ordinary Moderate, depending primarily on BPF access policy and whether an Oops is configured to panic the host. 5. One-sentence report phrase A suitably authorized local BPF program can pass a vmlinux BTF_KIND_VAR to bpf_snprintf_btf and trigger a NULL-derived invalid read in btf_var_show, causing a kernel Oops or panic without an established confidentiality, integrity, or privilege-escalation primitive. 6. Manual review recommendation NO MANUAL CHECK NEEDED The direct call path and primitive are established, and no UAF, write primitive, authorization bypass, or unresolved exploitation leverage remains. Product-specific BPF permissions and `panic_on_oops` affect exposure and availability severity but do not change the primitive class. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Fix NULL-ptr-deref in btf_var_show() [ Upstream Commit: e472ae0d97865e2021ee668a13eab64013aebf23 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e472ae0d97865e2021ee668a13eab64013aebf23 Changed files: kernel/bpf/btf.c kernel/trace/bpf_trace.c net/bpf/test_run.c kernel/bpf/syscall.c arch/x86/entry/syscall_64.c arch/x86/entry/entry_64.S 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=e472ae0d97865e2021ee668a13eab64013aebf23 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98063 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98063 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:L/PR:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: unknown Paranoid ActionableScore: 1 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).