From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98484][MODERATE REGULAR] netfilter: nf_tables: skip expired catchall elements on insert and delete Date: Fri, 23 Oct 2026 21:56:10 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98484 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: 2 X-AL-KERNEL-Commit: 2f07da3881525f7cbfed1ced2796c71a201505b9 List-Id: CVE: CVE-2026-98484 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: netfilter: nf_tables: skip expired catchall elements on insert and delete Commit: 2f07da3881525f7cbfed1ced2796c71a201505b9 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f07da3881525f7cbfed1ced2796c71a201505b9 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98484 Analysis date: Fri, 23 Oct 2026 21:56:10 -0400 ActionableScore: 4 ActionableScore lower bound: 2 Actionable bucket: Borderline / manual review required Manual review required: YES Summary: An expired nf_tables catchall element can remain hidden pending garbage collection while still blocking reinsertion or being selected for deletion, causing silent ruleset inconsistency and possible service disruption. For the CVSS the PR is H because the affected transaction requires CAP_NET_ADMIN or equivalent nftables management authority. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98484 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98484 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-2026-98484 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98484 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=MODERATE RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE) 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-672;*CWE-664;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 'An expired nf_tables catchall element can remain pending garbage collection while insertion and deletion still treat it as active. Reinsertion can fail with EEXIST or silently report success without installing a replacement, while deletion can retire the stale element instead of the fresh visible element. This can leave a catchall rule inactive for an arbitrarily long user controlled GC interval and can disrupt filtering, NAT, routing, or dependent services. For the CVSS the PR is H because triggering the highest score paranoid scenario requires CAP_NET_ADMIN or equivalent authority to modify the affected nftables ruleset. The issue is not directly network reachable because ordinary packet traffic does not perform the required set element transaction. Impact is availability loss from ruleset inconsistency. No memory corruption, information disclosure, privilege escalation, or code execution primitive is established. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 4.4 and the production ActionableScore returned 3 with recommendation Borderline / manual review required. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage IMPORTANT to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4. The independent weaker Aegis shadow evaluated CVSS 4.4 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review required (with actual score 3) MAYBE REMOTE DANGER NETFILTER LINUS LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=2 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=REQUIRED AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 4 * Paranoid score: 4 * Conservative CVSS:3.1: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L (2.3) * Paranoid CVSS:3.1: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H (4.4) * No floor or cap changed either score. * Final recommended bucket: **Borderline / manual review required**:: 2. Signal breakdown * +1 reproducible logical state inconsistency. Expired catchall elements remain eligible in insert and deactivate walks despite being excluded from lookup and dump. * +1 availability impact. Reinsertion may silently do nothing and deletion may select the stale element, leaving expected catchall behavior inactive until garbage collection. * Paranoid +2 deployment impact. A critical catchall used for filtering, NAT, or routing could cause substantial service disruption when the user controlled GC interval is long. * No memory corruption points. The expired element remains a valid allocated list object. * No UAF, OOB read, OOB write, arbitrary write, invalid read, or repeated lifetime mutation is established. * No authorization bypass points. The patch does not restore a capability check or change a kernel DENY decision into ALLOW. * No confidentiality or integrity points. A fail open firewall result is deployment dependent, and the supplied evidence does not establish unauthorized access to a protected resource. * No remote reachability points. Ordinary packets cannot invoke the affected nftables transaction paths. * No race penalty. The trigger is a deterministic timeout and garbage collection ordering condition rather than a narrow concurrency race. * CWE-672. Operation on a resource after expiration. * CWE-664. Improper control of a resource through its lifetime. * CWE-754. Improper check for unusual or exceptional conditions. 3. Reachability analysis The trigger uses the nftables Netlink control plane. A catchall element must first expire while remaining on catchall_list pending garbage collection. An authorized caller must then insert or delete a catchall element before the GC interval removes the stale entry. The insertion path reaches nft_setelem_catchall_insert. With NLM_F_EXCL it can return EEXIST for the expired element. Without NLM_F_EXCL it can report success while installing no replacement. The deletion path reaches nft_setelem_catchall_deactivate and can select the expired entry instead of the fresh visible entry. The affected operation requires CAP_NET_ADMIN or equivalent authority over the relevant network namespace. The supplied excerpt does not include the complete capability checks or establish whether the security relevant target ruleset is attacker controlled in an attacker reachable user and network namespace. Therefore HostAdminRequired and NamespaceScopedPrivilege remain UNKNOWN. RequiresHostUID0 is also UNKNOWN because CAP_NET_ADMIN rather than numeric UID alone governs the operation. No prior special hardware, device, race, or packet sequence is required. A timeout enabled catchall element and a sufficiently delayed GC pass are required. The GC interval is user tunable by an actor already authorized to configure the set. 4. Primitive and severity interpretation The exact defect is predicate drift across operations on the same catchall list. Lookup and dump ignore expired elements, while insertion and deactivation previously treated those elements as active transaction candidates. This creates a hidden stale semantic entry, not a dangling pointer or post lifetime memory access. PrimitiveClass is NONE. RealUAF is NO. There is no fixed stale storage write, active structured object corruption, repeated release, refcount mutation, or attacker controlled kernel memory primitive. The demonstrated consequence is silent nftables ruleset inconsistency and possible loss of expected catchall matching until garbage collection. The paranoid consequence is substantial availability disruption if the affected catchall controls critical filtering, NAT, routing, or dependent services. Information disclosure, protected state modification, privilege escalation, host panic, and code execution are not established. AuthorizationDecisionBypass is NO because no mandatory capability or access control guard is skipped. A policy configured by an already authorized nftables administrator may behave incorrectly, but this is not the B4 DENY to ALLOW authorization profile. ProtectedResourceImpact is NONE based on the supplied evidence. B4PendingReview and B4PendingConfirmed are both NO. ImportantCandidate is NO because no Class A or Class B primitive exists. AutoDowngradeAllowed is YES because no unresolved corruption, ownership, lifetime, or authorization primitive would be lost by downgrade. Manual review remains required for operational triage because the real impact depends on whether the catchall implements a critical fail closed networking policy. No supplied CVE advisory, exploit evidence, or public security discussion establishes consequences stronger than the patch description. The B5-R, B3-PENDING, B4-PENDING, active-state trust-boundary, checksum metadata, RNG integrity, and repeated-release profiles do not apply. 5. One-sentence report phrase An expired nf_tables catchall element can remain hidden pending garbage collection while still blocking reinsertion or being selected for deletion, causing silent ruleset inconsistency and possible service disruption. For the CVSS the PR is H because the affected transaction requires CAP_NET_ADMIN or equivalent nftables management authority. 6. Manual review recommendation MANUAL CHECK REQUIRED Review the affected catchall verdict, GC interval, namespace ownership, and whether loss of the rule creates a fail open policy or only temporary service degradation. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfilter: nf_tables: skip expired catchall elements on insert and delete Commit: 2f07da3881525f7cbfed1ced2796c71a201505b9 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f07da3881525f7cbfed1ced2796c71a201505b9 Commit description: nft_setelem_catchall_insert() looks up duplicates with nft_set_elem_active() only, while nft_set_catchall_lookup() and the dump path additionally skip expired elements. Once a catchall element with a timeout expires, this predicate drift makes it invisible to userspace dumps, yet it still blocks re-insertion: with NLM_F_EXCL the request fails with -EEXIST, and without it the request reports success but silently inserts nothing. The stale entry only goes away when the (user-tunable) gc interval elapses, so the catchall rule may silently stop matching for an arbitrarily long time after its first expiration. The delete path shows the same drift: nft_setelem_catchall_deactivate() picks the first active-next entry in the catchall list, so with an expired entry still pending GC it retires the stale entry instead of the fresh one, and it deactivates an element that userspace no longer sees instead of failing with -ENOENT. Align both walks with the lookup and dump predicates: only an element that is active and not expired counts as a duplicate or delete candidate, using the per-netns timestamp taken at transaction start, in line with the set backend .insert/.deactivate and catchall GC sync paths. Reported-by: TencentOS Corvus AI Cc: stable@vger.kernel.org Fixes: aaa3104 ("netfilter: nftables: add catch-all set element support") Assisted-by: CodeBuddy:Kimi-K3 Signed-off-by: Aohan Mei Signed-off-by: Pablo Neira Ayuso Signed-off-by: Greg Kroah-Hartman Changed files: net/netfilter/nf_tables_api.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=2f07da3881525f7cbfed1ced2796c71a201505b9 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98484 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98484 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: 2 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).