From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99283][MODERATE 7.0] netfilter: conntrack: tcp: use UNACK timeout for non-closing RST packets [ Upstream Date: Sat, 07 Nov 2026 22:14:29 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99283 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 0c6d33329960b2d884a399196c8403643d8a9de6 List-Id: CVE: CVE-2026-99283 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: netfilter: conntrack: tcp: use UNACK timeout for non-closing RST packets [ Upstream Commit: 0c6d33329960b2d884a399196c8403643d8a9de6 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c6d33329960b2d884a399196c8403643d8a9de6 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99283 Analysis date: Sat, 07 Nov 2026 22:14:29 -0400 ActionableScore: 4 ActionableScore lower bound: unknown Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: Remote crafted RST traffic can prematurely expire an established TCP conntrack entry, disrupting the connection or NAT mapping without causing memory corruption. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99283 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99283 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 7.0 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-2026-99283 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99283 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE_KPANIC, Aegis: MODERATE) 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-664;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'A logic error in TCP conntrack timeout selection can assign the short CLOSE timeout to an in-window but non-exact RST even though the conntrack state remains ESTABLISHED. A second crafted RST can arrive while challenge ACK responses are rate limited, allowing the entry to expire while both TCP endpoints still consider the connection established. This can disrupt the affected connection through firewall state loss or removal of a NAT mapping, but there is no supported memory corruption, information disclosure, or privilege escalation primitive. For the CVSS the PR:N value is selected because crafted packets can trigger the condition lacking a local user context, while AC:H reflects the need to identify the flow, place the RST sequence inside the valid window, and satisfy challenge ACK timing terms. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.9 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 3.7 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE REMOTE NETFILTER LEAK NETWORK LINUS KPANIC PACKET - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 4. * Conservative score: 4; no floor or cap applied. * Raw paranoid score: 4. * Paranoid score: 4; stronger memory-corruption or host-wide availability effects are unsupported. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown * +2 Remote/net-reachable trigger: crafted in-window, non-exact RST packets reach conntrack processing without attacker privilege. * +1 Common packet-processing path: TCP conntrack timeout selection is part of an active firewall/NAT data path. * +1 Availability impact: premature conntrack expiration can disrupt the affected connection or remove its NAT mapping while endpoints remain established. * 0 Timing penalty: sequence-window knowledge and challenge-ACK timing increase complexity, but the evidence does not establish a narrow, uncontrollable race warranting −1. * No memory corruption, UAF, OOB access, disclosure, authorization bypass, privilege escalation, or host-wide kernel crash is shown. * No second availability point: repeatability or possible NAT impact is not distinct from the same connection-state loss. 3. Reachability analysis A remote unauthenticated sender able to identify the flow, choose an in-window RST sequence, and exploit challenge-ACK rate limiting can trigger the timeout mismatch. No UID 0, capability, namespace privilege, or attacker-controlled privileged setup is required. Conntrack and possibly NAT/firewall deployment are environmental prerequisites. Trigger complexity is elevated, but retries are network-driven and no special hardware or rare execution mode is involved. 4. Primitive and severity reading The primitive is a semantic conntrack-state inconsistency: `new_state` remains ESTABLISHED, but vulnerable code assigns the short CLOSE timeout based solely on the RST packet type. The later timer consumes this incorrect active state and expires the entry. This is CLASS_C invalid-state/availability behavior, not active memory corruption. The demonstrated effect is per-flow disruption; host panic, broad policy bypass, protected-state corruption, and stronger integrity effects remain unproven. Therefore it is not an Important candidate and may be downgraded after product exposure review. 5. One-sentence report phrase Remote crafted RST traffic can prematurely expire an established TCP conntrack entry, disrupting the connection or NAT mapping without causing memory corruption. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm affected-product conntrack/NAT exposure and whether the practical packet-sequence and timing requirements permit meaningful repeated disruption. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfilter: conntrack: tcp: use UNACK timeout for non-closing RST packets [ Upstream Commit: 0c6d33329960b2d884a399196c8403643d8a9de6 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c6d33329960b2d884a399196c8403643d8a9de6 Changed files: net/netfilter/nf_conntrack_proto_tcp.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=0c6d33329960b2d884a399196c8403643d8a9de6 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99283 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99283 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: unknown 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: YES Published priority for this report (same as in Subject): MODERATE 7.0 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).