From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53269][MODERATE REGULAR] netfilter: synproxy: add mutex to guard hook reference counting [ Upstream Date: Thu, 25 Jun 2026 10:52:42 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53269 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: 1 X-AL-KERNEL-Commit: 0ec9ddc1bda261a2c57636c74c8b4e53000102c9 List-Id: CVE: CVE-2026-53269 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: netfilter: synproxy: add mutex to guard hook reference counting [ Upstream Commit: 0ec9ddc1bda261a2c57636c74c8b4e53000102c9 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0ec9ddc1bda261a2c57636c74c8b4e53000102c9 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53269 Analysis date: Thu, 25 Jun 2026 10:52:42 -0400 ActionableScore: 4 ActionableScore lower bound: 1 Actionable bucket: Borderline manual review recommended Manual review required: YES Summary: A race in netfilter SYNPROXY hook reference counting can desynchronize hook registration during concurrent iptables and nftables rule updates, potentially causing SYNPROXY malfunction or DoS when an attacker can modify firewall rules. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53269 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53269 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-2026-53269 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H';CWE-362;CWE-667;CWE-911;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'SYNPROXY hook registration is controlled by reference counters that can be updated concurrently from the iptables target path and the nftables expression path. A race during concurrent rule add or delete operations can leave the hook registration state inconsistent with the active SYNPROXY users, causing premature hook unregister, duplicate registration attempts, or lost reference count updates. For the CVSS the PR:L is used in the paranoid score because an attacker may only need delegated CAP_NET_ADMIN in a network namespace or a reduced capability service account that can update iptables or nftables rules. The issue is not directly network reachable because packet traffic alone does not trigger the race. Impact is mainly denial of service or SYNPROXY policy malfunction, with limited integrity impact possible if expected SYNPROXY processing is bypassed due to hook state desynchronization.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended (with actual score 3) YES REMOTE LOCK SIMPLEFIX NETFILTER RACE IPV6 DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 4 * Final recommended bucket: **Borderline manual review recommended**:: ## 2. Signal breakdown Conservative signals: * Availability impact realistic: +1. A refcount race can leave SYNPROXY hook registration state inconsistent, causing SYNPROXY malfunction or failed hook lifecycle behavior. * Common networking or netfilter path: +1. The affected code manages netfilter hooks used by SYNPROXY, though the trigger is control-plane rule updates rather than packet traffic. * Hard or unreliable race: -1. The issue requires concurrent add or delete operations from iptables and nftables frontends. * Requires CAP_NET_ADMIN in typical deployments: -2. Adding or removing SYNPROXY targets or expressions normally requires administrative network configuration privileges. Paranoid additional interpretation: * Local delegated trigger: +1. In some environments, CAP_NET_ADMIN may be delegated to containers, network namespaces, or firewall-management service accounts, making PR:L more realistic than full host-root. * Integrity impact plausible: +1. If hook reference accounting is desynchronized, expected SYNPROXY packet handling may be bypassed or disabled unexpectedly. * Cross-boundary policy concern: +1. The bug can affect packet filtering or SYNPROXY enforcement state, which is security policy rather than only local process behavior. No strong memory corruption signal is counted. The patch shows serialization of hook reference counters, not UAF, OOB write, double free, callback corruption, or attacker-controlled object reuse. ## 3. Reachability analysis The bug is triggered by concurrent control-plane operations that add or remove SYNPROXY through iptables and nftables. It is not directly network reachable because packet traffic alone does not exercise the race. In typical host deployments the attacker needs CAP_NET_ADMIN, so the conservative score is low. In containerized or delegated administration environments, a reduced-privilege user or service account may be able to update nftables or iptables rules, which makes the paranoid PR:L interpretation reasonable. ## 4. Severity interpretation This behaves more like a borderline Moderate control-plane race than an Important memory-corruption vulnerability. The realistic impact is SYNPROXY hook lifecycle inconsistency, possible DoS, or limited packet-filtering policy malfunction. There is no demonstrated privilege escalation primitive and no concrete memory corruption primitive in the patch. ## 5. One-sentence report phrase A race in netfilter SYNPROXY hook reference counting can desynchronize hook registration during concurrent iptables and nftables rule updates, potentially causing SYNPROXY malfunction or DoS when an attacker can modify firewall rules. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED. Reason: not memory corruption and not remotely packet-triggered, but it is a netfilter hook lifecycle race with possible security-policy impact under delegated CAP_NET_ADMIN environments. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfilter: synproxy: add mutex to guard hook reference counting [ Upstream Commit: 0ec9ddc1bda261a2c57636c74c8b4e53000102c9 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0ec9ddc1bda261a2c57636c74c8b4e53000102c9 Changed files: net/netfilter/nf_synproxy_core.c net/netfilter/nf_conntrack_zones.h net/netfilter/nf_synproxy.h 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=0ec9ddc1bda261a2c57636c74c8b4e53000102c9 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53269 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53269 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:H/PR:H/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H The Best / paranoid CVSS score: 5.3 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: 1 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).