From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98064][LOW] bpf: Fix NULL-ptr-deref when showing a void BTF type [ Upstream Date: Sat, 26 Sep 2026 16:24:16 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98064 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 717abdfd1d559d01fdd102023f0a990fb0437240 List-Id: CVE: CVE-2026-98064 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: bpf: Fix NULL-ptr-deref when showing a void BTF type [ Upstream Commit: 717abdfd1d559d01fdd102023f0a990fb0437240 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=717abdfd1d559d01fdd102023f0a990fb0437240 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98064 Analysis date: Sat, 26 Sep 2026 16:24:16 -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-2026-98064 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98064 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: LOW 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-2026-98064 LOW https://www.kernelcve.org/list/?q=CVE-2026-98064 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:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in btf_modifier_show can occur when a BPF program passes a const void BTF type to bpf_snprintf_btf. The modifier resolves to the void BTF type which has no show operation, and the kernel dereferences the missing operation while formatting the BTF value. This can crash the host kernel and cause a local denial of service. The issue is not directly network reachable. For the CVSS the PR:L paranoid assessment assumes an attacker can load and execute a BPF program through delegated BPF access, a capable service account, or comparable non full administrative access. The normal deployment often restricts BPF program loading and test execution to highly privileged users. There is no evidence in the patch of a use after free, out of bounds access, arbitrary write, information disclosure, or privilege escalation primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES KASAN NULLPTR BPF LINUS INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO 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 * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable kernel crash or strong DoS. A BPF program can reach `btf_modifier_show()` through `bpf_snprintf_btf()` with a `const void` BTF type, causing a NULL function-pointer dereference in the kernel. * No UAF or lifetime violation is established. The resolved BTF type is valid as a type representation, but it has no `show` handler. * No controlled reclaim, object replacement, refcount mutation, arbitrary write, OOB access, callback control, disclosure, or privilege-escalation primitive is established. * No remote-reachability point. The supplied call trace reaches the bug through the local `bpf()` syscall and BPF program test-run path. * No local-unprivileged-trigger point. The supplied evidence does not establish that an ordinary unprivileged user can load the required BPF program and execute the complete trigger path. * No privilege penalty is applied. The complete required BPF privilege boundary is not fully established, therefore host-admin-equivalent access cannot be positively concluded. * No extra availability point. The demonstrated kernel crash is already counted once. * No paranoid increment. A more severe interpretation would require an unsupported memory-corruption or privilege-boundary primitive. 3. Reachability analysis The demonstrated trigger requires a BPF program that invokes `bpf_snprintf_btf()` with a BTF type ID representing `const void`, followed by execution through the BPF test-run path shown in the call trace. BPF program loading and test execution are commonly privilege-gated. Depending on kernel configuration and program type, relevant controls can include `CAP_BPF`, `CAP_PERFMON`, `CAP_SYS_ADMIN`, BPF LSM policy, and root-controlled unprivileged-BPF settings. The supplied patch does not establish that the complete load, helper use, and test-run sequence is available to an ordinary unprivileged user, a container user, or a namespace-scoped capability holder. There is no network packet path, device prerequisite, special hardware requirement, race, async lifetime transition, or prior host-created object demonstrated by the patch. The vulnerability is a local BPF control-plane crash condition. 4. Primitive and severity interpretation The exact primitive is an invalid NULL function-pointer dereference. `btf_modifier_show()` removes BTF modifiers and can resolve `const void` to the void BTF type. The void type has no `kind_ops` entry and therefore no `show` operation. The vulnerable code dereferences `btf_type_ops(t)->show` without checking whether the operation table exists. This is not an active structured-object UAF, fixed stale storage issue, repeated release, refcount error, ownership violation, or security-boundary bypass. No first lifetime operation can free an object, and no second lifetime or refcount mutation exists. The demonstrated consequence is local kernel crash or DoS. Confidentiality, integrity, privilege escalation, controlled kernel memory corruption, and remote impact are speculative and unsupported by the supplied evidence. The issue is classified as CLASS_C because it is a crash-capable invalid-state and NULL-dereference condition without an independently useful corruption primitive. ImportantCandidate is NO because there is no meaningful unresolved leverage beyond the crash. AutoDowngradeAllowed is YES because the patch-supported behavior is constrained to a NULL dereference and no concrete memory-corruption or authorization primitive remains. Likely operational severity is low to ordinary Moderate, depending on whether the evaluated product delegates the required BPF access to non-administrative users. 5. One-sentence report phrase A privileged BPF program can pass a const void BTF type to bpf_snprintf_btf and trigger a NULL pointer dereference in btf_modifier_show, causing a local kernel denial of service. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch demonstrates a NULL dereference and kernel-crash condition only, with no UAF, write primitive, disclosure path, authorization bypass, or privilege-escalation mechanism. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Fix NULL-ptr-deref when showing a void BTF type [ Upstream Commit: 717abdfd1d559d01fdd102023f0a990fb0437240 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=717abdfd1d559d01fdd102023f0a990fb0437240 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=717abdfd1d559d01fdd102023f0a990fb0437240 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98064 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98064 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:H/UI:N/S:U/C:N/I:N/A:H 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).