From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72418][MODERATE REGULAR] netfilter: nf_conncount: prevent connlimit drops for early confirmed ct [ Upstream Date: Sun, 16 Aug 2026 03:57:47 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72418 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: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 000ac6830b56499d6b65fd91486ce6689eb02be4 List-Id: CVE: CVE-2026-72418 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: netfilter: nf_conncount: prevent connlimit drops for early confirmed ct [ Upstream Commit: 000ac6830b56499d6b65fd91486ce6689eb02be4 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=000ac6830b56499d6b65fd91486ce6689eb02be4 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72418 Analysis date: Sun, 16 Aug 2026 03:57:47 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline Moderate / Manual review recommended Manual review required: YES Summary: A logic regression in nf_conncount can cause connlimit to falsely drop valid early-confirmed connections, allowing a remote peer to cause service-level denial of service on systems using affected connlimit rules. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72418 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72418 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-72418 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-682;CWE-697;CWE-703;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'nf_conncount can incorrectly drop packets for valid connections when connlimit is used for soft limiting and a new connection reuses a socket in TIME_WAIT. The confirmed conntrack entry may be treated as already counted, garbage collection can remove the old TIME_WAIT entry, and the active count can fall to 0 which xt_connlimit then mishandles. For the CVSS the PR:N is used because a remote peer only needs network reachability to the protected service in affected configurations. The issue is network reachable through normal connection attempts, but exploitation depends on connlimit rules and connection reuse timing. Impact is denial of service for legitimate connection establishment, not kernel memory corruption or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate / Manual review recommended (with actual score 4) SKIP CVE-2026-72418 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 69894e5b4c5e28cda5f32af33d4a92b7a4b93b0e YES NO NO unknown MAYBE REMOTE NETFILTER SKB TEST PACKET INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline Moderate / Manual review recommended**:: ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2 A remote peer can influence the affected path by making normal connection attempts to a service protected by connlimit. * Common networking core path or packet-processing path: +1 The bug is in netfilter conntrack / connlimit packet-processing logic. * Availability impact realistic: +1 Valid connections can be falsely rejected, causing service-level DoS. * Hard or configuration-dependent trigger: -1 The issue requires connlimit rules plus early-confirmed conntrack states such as TIME_WAIT reuse or similar setup-packet behavior. Paranoid difference: * The -1 reliability/configuration penalty can be omitted because the commit notes testing with slowhttptest and local/external HTTP scenarios, suggesting realistic reproducibility in affected configurations. No added signals for memory corruption, UAF, LPE, confidentiality, or integrity. The patch shows a logic/counting regression, not a kernel memory-safety primitive. ## 3. Reachability analysis A remote unauthenticated client can potentially trigger the behavior if it can reach a service behind nft_connlimit or xt_connlimit rules. The attacker does not need privileges on the target host, but the target must already be configured with affected connlimit policy. Namespaces mainly affect who can configure the rules, not who can trigger the packet path once the rules exist. This is not default-enabled for all systems because it depends on connlimit usage, but it is realistic for firewalls, web servers, OVS zones, or soft-limiting deployments. ## 4. Severity interpretation This behaves like a network-reachable Moderate availability issue, not an Important-class kernel vulnerability. There is no evidence of memory corruption, privilege escalation, information disclosure, arbitrary write, or kernel crash. The practical impact is false rejection of valid connections and service degradation under specific connlimit and conntrack-state conditions. ## 5. One-sentence report phrase A logic regression in nf_conncount can cause connlimit to falsely drop valid early-confirmed connections, allowing a remote peer to cause service-level denial of service on systems using affected connlimit rules. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is recommended because the issue is network-triggerable and depends heavily on firewall policy and deployment context, but it is not a memory corruption or privilege-escalation candidate. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfilter: nf_conncount: prevent connlimit drops for early confirmed ct [ Upstream Commit: 000ac6830b56499d6b65fd91486ce6689eb02be4 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=000ac6830b56499d6b65fd91486ce6689eb02be4 Changed files: net/netfilter/nf_conncount.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=000ac6830b56499d6b65fd91486ce6689eb02be4 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72418 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72418 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:H/PR:N/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.9 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: 3 Paranoid ActionableScore: 4 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).