From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72348][IMPORTANT] netfilter: ip6tables: mark malformed IPv6 extension headers for hotdrop [ Upstream Date: Sun, 16 Aug 2026 09:03:39 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72348 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: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: f16d856b6af5fd0e7cb0b0212f70825b599ef72e List-Id: CVE: CVE-2026-72348 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: netfilter: ip6tables: mark malformed IPv6 extension headers for hotdrop [ Upstream Commit: f16d856b6af5fd0e7cb0b0212f70825b599ef72e Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f16d856b6af5fd0e7cb0b0212f70825b599ef72e Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72348 Analysis date: Sun, 16 Aug 2026 09:03:39 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate. Network reachable firewall policy bypass that should not be auto closed. Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72348 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72348 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-2026-72348 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N';CWE-693;*CWE-20;CWE-284;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '6.5';DESCR 'Malformed IPv6 AH, HBH, or RT extension headers can be treated as a rule mismatch in ip6tables instead of being dropped when the advertised extension header length is larger than the available packet data. A remote attacker can send such malformed IPv6 packets to bypass rules that were intended to match and drop packets with these extension headers. For the CVSS the PR:N is used because no local account or code execution is needed when the filtered IPv6 traffic path is reachable. The issue is network reachable but only affects systems with relevant ip6tables IPv6 extension header match rules. Impact is primarily firewall policy bypass. In the paranoid score this is treated as possible limited confidentiality and integrity impact because traffic that should have been blocked may reach protected services.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES REMOTE SIMPLEFIX NETFILTER NETWORK SKB LINUS IPV6 KPANIC PACKET NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 1. ActionableScore * Conservative score: 5 * Paranoid score: 6 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate. Network reachable firewall policy bypass that should not be auto closed. 2. Signal breakdown * Remote reachable / network-triggerable: +2. A remote sender can craft malformed IPv6 packets with AH, HBH, or RT extension headers. * Cross-boundary isolation/policy bypass: +1. The bug can bypass ip6tables rules intended to drop packets with these IPv6 extension headers. * Common networking core path or packet-processing path: +1. This is netfilter IPv6 packet filtering logic. * Integrity impact plausible: +1. Traffic that should have been blocked by firewall policy may be accepted. * Confidentiality impact plausible, paranoid only: +1. If bypassed rules protect internal services or restricted traffic paths, limited confidentiality impact is plausible. * No memory corruption signal. The patch adds length validation and hotdrop behavior, not lifetime, UAF, OOB write, or object corruption handling. * No strong DoS signal. The main impact is policy bypass, not crash or resource exhaustion. 3. Reachability analysis A remote attacker can trigger the affected path by sending malformed IPv6 packets if the target routes the traffic through ip6tables rules using the affected AH, HBH, or RT matches. No local account is required, so PR:N is appropriate. The issue is configuration dependent because it matters only when such ip6tables IPv6 extension header rules are deployed. However, netfilter packet filtering is a common security boundary, so this should not be treated as a rare unreachable subsystem. Namespaces or containers do not reduce the remote trigger requirement, but they may affect where such filtering rules are installed. 4. Severity interpretation This behaves like an actionable Moderate issue rather than ordinary Low or pure correctness cleanup. It is not an Important memory corruption candidate because there is no UAF, OOB write, type confusion, refcount bug, or arbitrary write. The realistic impact is remote firewall rule bypass for malformed IPv6 extension header packets. The paranoid score reaches 6 because limited confidentiality and integrity impact are defensible when bypassed firewall policy protects access to sensitive services. 5. One-sentence report phrase Malformed IPv6 AH, HBH, or RT extension headers may be treated as ip6tables rule mismatches instead of hotdrops, allowing a remote attacker to bypass rules intended to drop such packets when the relevant IPv6 extension header matches are configured. 6. Manual review recommendation MANUAL CHECK REQUIRED. The issue is network reachable and affects firewall policy enforcement, so it should not be auto-closed even though the patch does not indicate memory corruption. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfilter: ip6tables: mark malformed IPv6 extension headers for hotdrop [ Upstream Commit: f16d856b6af5fd0e7cb0b0212f70825b599ef72e Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f16d856b6af5fd0e7cb0b0212f70825b599ef72e Changed files: net/ipv6/netfilter/ip6t_ah.c net/ipv6/netfilter/ip6t_hbh.c net/ipv6/netfilter/ip6t_rt.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=f16d856b6af5fd0e7cb0b0212f70825b599ef72e ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72348 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72348 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:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N The Best / paranoid CVSS score: 6.5 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: 5 Paranoid ActionableScore: 6 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).