From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-97598][MODERATE REGULAR] ipv4: fib: bound automatic table ID allocation Date: Fri, 25 Sep 2026 13:15:46 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-97598 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: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: bc8d01d856db106f284b19961af6112e10c3e3b4 List-Id: CVE: CVE-2026-97598 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: ipv4: fib: bound automatic table ID allocation Commit: bc8d01d856db106f284b19961af6112e10c3e3b4 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bc8d01d856db106f284b19961af6112e10c3e3b4 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97598 Analysis date: Fri, 25 Sep 2026 13:15:46 -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-2026-97598 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97598 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-97598 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97598 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-400;CWE-407;CWE-770;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'IPv4 automatic routing table allocation can consume excessive CPU while holding RTNL because fib_empty_table searches sequential table IDs and repeatedly walks growing hash chains for dense table sets. A local actor able to create many IPv4 policy rules with automatic table selection can delay network control plane operations and potentially cause soft lockups or denial of service. For the CVSS the PR:L is used for the paranoid score because CAP_NET_ADMIN may be delegated to a service account, container root, or a user in a network namespace. The issue is not directly network reachable and is triggered through local routing rule configuration rather than packet traffic. Impact is denial of service only. No memory corruption, information disclosure, integrity impact, or privilege escalation primitive is indicated.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES REMOTE NETWORK DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED 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 control plane denial of service. A dense set of IPv4 FIB table IDs can cause fib_empty_table to perform a very long sequential search while RTNL is held. This can stall routing and network configuration operations and may cause a CPU soft lockup. * No remote reachability bonus. The vulnerable operation is performed through local rtnetlink rule configuration, not packet processing. * No local unprivileged trigger bonus. CAP_NET_ADMIN is relevant, but the supplied material does not establish that an ordinary attacker can complete the full setup and trigger sequence below host administrative privilege. * No memory corruption, UAF, OOB access, invalid free, refcount misuse, disclosure, integrity impact, authorization bypass, or privilege escalation primitive is established. * No resource leak signal. The problem is algorithmic CPU consumption and prolonged RTNL lock holding, not an unreleased resource. * No extra Availability point. The same RTNL stall and possible soft lockup are already represented by the single DoS point. * No negative host-admin penalty. Host-admin-equivalent privilege is not positively established, so a -2 penalty is not justified. * No namespace reachability bonus. Rtnetlink capability checks may be namespace-aware, but the supplied evidence does not prove that an attacker can create a suitable namespace and complete all required operations while causing meaningful host-wide RTNL contention. 3. Reachability analysis The direct trigger is local IPv4 policy-routing configuration using automatic table selection, for example a rule using table 0. The attacker must create a dense set of table IDs and then invoke automatic allocation so fib_empty_table scans occupied IDs while RTNL is held. The relevant configuration interface normally requires CAP_NET_ADMIN. The supplied patch does not show the exact rtnetlink capability check or prove whether a user with CAP_NET_ADMIN only in an attacker-created network namespace can complete the full high-cost sequence and cause host-wide impact through the global RTNL lock. Therefore HostAdminRequired and NamespaceScopedPrivilege remain UNKNOWN. No prior hardware, firmware, boot parameter, or special device is required. The legacy automatic table allocation path is explicitly described as IPv4-only, undocumented, not covered by selftests, and unused by NetworkManager and systemd. This reduces practical exposure, but no score penalty is applied because the path can still be directly invoked through low-level routing configuration. 4. Primitive and severity interpretation The established primitive is excessive algorithmic work under RTNL. The function sequentially probes table IDs and repeatedly performs hash-table lookups. A dense table-ID allocation pattern creates increasing hash-chain traversal cost while RTNL remains locked. This is not a lifetime bug, UAF, stale-object bug, ownership violation, memory corruption issue, or security-boundary bypass. There is no attacker-controlled kernel memory corruption primitive after excluding the availability effect. The demonstrated consequence is local network control-plane denial of service through prolonged RTNL lock contention, high CPU consumption, and possible soft lockups. PrimitiveClass is NONE because the patch establishes no meaningful corruption, lifetime, authorization, ownership, or semantic reinterpretation primitive. ImportantCandidate is NO because the issue is a bounded-resource and locking DoS without evidence of cross-boundary resource exhaustion, persistent state damage, confidentiality impact, integrity impact, or privilege escalation. AutoDowngradeAllowed is YES because no unresolved concrete kernel-corruption or security-boundary primitive would be discarded by ordinary Moderate handling. 5. One-sentence report phrase IPv4 automatic routing table allocation can hold RTNL for excessive time when dense table IDs force repeated hash-chain scans, causing local network control-plane denial of service and possible CPU soft lockups. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Verify the exact capability check and whether an untrusted user with CAP_NET_ADMIN in an attacker-created network namespace can create the required dense table set and cause meaningful host-wide RTNL contention. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ipv4: fib: bound automatic table ID allocation Commit: bc8d01d856db106f284b19961af6112e10c3e3b4 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bc8d01d856db106f284b19961af6112e10c3e3b4 Commit description: fib_empty_table() probes every table ID from 1 until it finds a free one. IPv4 tables are stored in a 256-bucket hash table, so a dense set of IDs makes each probe walk a growing hash chain while RTNL is held. Automatic table assignment ("ip rule ... table 0") is an IPv4-only legacy path. Bound the automatically allocated ID to 4096 so the RTNL hold stays bounded, without changing lookups of explicitly specified table IDs. This changes user-visible behavior. A table-0 rule previously received the lowest free ID in 1..RT_TABLE_MAX (0xFFFFFFFF). After this patch the search stops at 4096 and the rule add fails with ENOBUFS if that range is fully occupied. Explicit table IDs above 4096 remain usable. The automatic path is unused in practice: it is IPv4-only, not documented by ip-rule, uncovered by kernel selftests, and both NetworkManager and systemd refuse table 0. Fixes: b801f54 ("[NET]: Increate RT_TABLE_MAX to 2^32") Cc: stable@vger.kernel.org Reported-by: Vega Suggested-by: Ido Schimmel Signed-off-by: Zihan Xi Reviewed-by: Ido Schimmel Reviewed-by: Petr Vorel Link: https://patch.msgid.link/6f2f2a7a136aee005512a2e1ac8ede62ac8c7bb6.1788258884.git.zihanx@nebusec.ai Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/ipv4/fib_rules.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=bc8d01d856db106f284b19961af6112e10c3e3b4 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97598 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97598 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: 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).