From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98044][LOW] bpf: Reject legacy packet loads from callbacks [ Upstream Date: Sat, 26 Sep 2026 14:40:25 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98044 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: 0 X-AL-KERNEL-Commit: 3484a99303912db62428494a9061212049027e57 List-Id: CVE: CVE-2026-98044 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: bpf: Reject legacy packet loads from callbacks [ Upstream Commit: 3484a99303912db62428494a9061212049027e57 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3484a99303912db62428494a9061212049027e57 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98044 Analysis date: Sat, 26 Sep 2026 14:40:25 -0400 ActionableScore: 1 ActionableScore lower bound: 0 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-2026-98044 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98044 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-2026-98044 LOW https://www.kernelcve.org/list/?q=CVE-2026-98044 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:H/UI:N/S:U/C:N/I:N/A:H';CWE-617;CWE-703;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'A logic error in the BPF verifier allows legacy BPF_LD_ABS or BPF_LD_IND packet loads reached from a synchronous callback to enter an inconsistent precision backtracking path. The synthesized failure return has R0 set to zero without a corresponding instruction, and precision tracking can reach the callback call while R0 is still requested. This triggers the callback unexpected regs verifier warning and causes BPF_PROG_LOAD to fail with EFAULT. For the CVSS the PR:H reflects that the trigger requires a privileged BPF program loader with capabilities such as CAP_BPF or CAP_SYS_ADMIN. The issue is local and is not directly network reachable. The normal impact is limited availability loss for the crafted program load, while systems configured to panic on kernel warnings may experience a kernel crash and system wide denial of service. No UAF, out of bounds access, information disclosure, or write primitive is visible in the affected path.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) SKIP CVE-2026-98044 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE OOB BPF IMPROVEONLY LINUS PACKET - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 ActionableScoreLower=0 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 0 * Conservative score: 0 * Raw paranoid score: 1 * Paranoid score: 1 * No floor or cap changed either score. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown Conservative signals: * +0 reachable verifier warning and rejected BPF_PROG_LOAD. The demonstrated normal consequence is a warning and EFAULT affecting the crafted program load. * +0 memory-corruption primitive. No UAF, OOB access, stale object, write primitive, ownership violation, or lifetime corruption is established. * +0 remote reachability. Triggering requires a local BPF program-loading operation. * +0 availability. WARN_ON behavior is not inherently fatal. Paranoid-only signal: * +1 reliable kernel crash or strong DoS under a panic-on-warning policy. The reachable verifier warning can become a host-wide panic when warnings are configured as fatal. Negative and non-awarded signals: * No privilege penalty was applied because privileged BPF loading is established, but host-admin-equivalent privilege versus a reduced delegated capability is not fully resolved. * Local unprivileged reachability was not awarded. * Strong or weak exploitation leverage was not awarded. * Confidentiality and integrity were not awarded. * No additional availability point was awarded because the possible panic is the only availability consequence. * Controlled reclaim, arbitrary write, information disclosure, privilege escalation, and security-boundary bypass are not demonstrated. 3. Reachability analysis A local privileged BPF program loader can submit a program containing legacy BPF_LD_ABS or BPF_LD_IND instructions in a callback call chain. Verification alone reaches the defect, so successful attachment, packet processing, or network traffic is unnecessary. The input establishes privilege gating but does not identify the complete capability checks or whether CAP_BPF, CAP_SYS_ADMIN, or another host-scoped combination is required. HostAdminRequired and NamespaceScopedPrivilege therefore remain UNKNOWN. There is no evidence that an ordinary user can complete the loading operation inside an attacker-created namespace. No race, special hardware, device state, or remote endpoint is involved. The deprecated instruction form is a program-content prerequisite, not an independently scored rare-subsystem penalty. 4. Primitive and severity interpretation The exact defect is inconsistent verifier-state modeling. A synthesized failed packet-load path assigns R0 without a corresponding instruction, after which precision backtracking reaches a callback boundary with an unexpected register request. The resulting primitive is a reachable internal verifier warning followed by EFAULT. This is CLASS_C invalid-state or DoS behavior. It is not a UAF and does not perform a repeated release or refcount mutation. The normal demonstrated consequence is rejection of the attacker-supplied program. A kernel panic is plausible only when the system converts warnings into fatal events. There is no useful primitive remaining after excluding the warning or possible panic. ImportantCandidate is therefore NO, and AutoDowngradeAllowed is YES. 5. One-sentence report phrase A privileged local BPF program loader can trigger an internal verifier warning and BPF_PROG_LOAD failure by placing deprecated packet-load instructions in a callback call chain, with kernel panic possible on systems configured to treat warnings as fatal. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch establishes a privilege-gated verifier warning without memory corruption, authorization bypass, disclosure, or unresolved lifetime primitive. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Reject legacy packet loads from callbacks [ Upstream Commit: 3484a99303912db62428494a9061212049027e57 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3484a99303912db62428494a9061212049027e57 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=3484a99303912db62428494a9061212049027e57 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98044 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98044 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:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.4 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: 0 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).