From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72423][MODERATE 7.0] bpf: Guard conntrack opts error writes [ Upstream Date: Sun, 16 Aug 2026 04:01:12 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72423 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 6 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: dd74c80203842a21b2ebb9f70d1260d9aa20fa05 List-Id: CVE: CVE-2026-72423 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: bpf: Guard conntrack opts error writes [ Upstream Commit: dd74c80203842a21b2ebb9f70d1260d9aa20fa05 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dd74c80203842a21b2ebb9f70d1260d9aa20fa05 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72423 Analysis date: Sun, 16 Aug 2026 04:01:12 -0400 ActionableScore: 6 ActionableScore lower bound: 4 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A verifier range mismatch in BPF conntrack kfunc wrappers can allow `opts.error` to be written outside the checked `opts__sz` range, creating a constrained kernel out-of-bounds write reachable by privileged XDP or TC BPF programs. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72423 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72423 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-2026-72423 MODERATE 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:H/I:H/A:H';*CWE-787;*CWE-20;CWE-119;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'BPF conntrack lookup and allocation kfuncs can write opts.error even when opts__sz does not cover that field. The verifier only checks the memory range described by opts__sz, so the unconditional error write can land outside the verifier checked range and become an out-of-bounds kernel memory write. For the CVSS the PR:L is used for the paranoid score because delegated BPF or network administration capabilities may be available to non-root service accounts or containerized operators in some deployments. The issue is not directly network reachable because an attacker must be able to load or run an affected XDP or TC BPF program. Network traffic may exercise an already attached program, but packet input alone is not the security boundary. Impact is at least local denial of service and in the worst still-defensible case may include confidentiality and integrity impact due to memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) YES REMOTE INIT BPF SIMPLEFIX NETFILTER LINUS INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 6 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative scoring: * Generic memory corruption: +2. The wrappers can write `opts->error` outside the verifier checked range when `opts__sz` is smaller than `offsetofend(struct bpf_ct_opts, error)`. * Reliable kernel crash / strong DoS: +1. An out of bounds kernel write from a BPF kfunc path can plausibly crash the kernel, even if payload and target are constrained. * Availability impact realistic: +1. Once a privileged BPF program is loaded and attached, the failing helper path can be exercised repeatedly. * Requires admin/root/CAP_* in typical deployments: -2. XDP/TC BPF loading and attachment normally require privileged BPF and network capabilities. * Corruption primitive constrained: -1. The written value is `PTR_ERR(ret)`, mostly kernel-derived errno data, not an arbitrary attacker chosen payload. Conservative total: 4. Paranoid scoring: * Generic memory corruption: +2. This is an out of bounds kernel write caused by verifier range mismatch. * Privilege escalation plausible: +2. BPF verifier boundary bypasses historically deserve manual review because even constrained writes can sometimes be composed with verifier state, stack, or adjacent object assumptions. * Reliable kernel crash / strong DoS: +1. The bug can force an invalid kernel write on helper error paths. * Broad/default/common subsystem: +1. BPF plus netfilter conntrack kfuncs are security-sensitive kernel infrastructure, even if access is capability gated. * Corruption primitive constrained: -1. The write target and payload are not shown to be arbitrary. * BPF privilege gating cap applied. Because affected product assumptions gate BPF behind CAP_BPF/CAP_NET_ADMIN/root-controlled policy, paranoid score is capped at 6 without proven unprivileged reachability or arbitrary write. Paranoid total after cap: 6. ## 3. Reachability analysis The bug is triggered by a BPF program calling conntrack lookup or allocation kfuncs with an `opts__sz` that does not cover `opts->error`, while the internal helper returns an error. In typical deployments this requires the ability to load and attach XDP or TC BPF programs, so the conservative privilege model is privileged local access with CAP_BPF and CAP_NET_ADMIN or equivalent root control. Namespaces and containers matter if BPF or network administration capabilities are delegated to a reduced-privilege service account or container root. In that model the issue is more actionable because the attacker may not be full host root, but still can reach the affected helper path. The issue is not directly network reachable. Network traffic may exercise an already attached program, but packets alone do not cross the security boundary unless the attacker can also influence the BPF program or its configuration. ## 4. Severity interpretation This is not an ordinary resource leak or validation-only cleanup. The patch fixes a verifier checked range mismatch that can produce an out of bounds kernel write. Realistic exploitation is constrained by privileged BPF access and by the limited errno-style write payload, so the conservative interpretation is borderline manual-review Moderate. The paranoid interpretation is Actionable Moderate because BPF verifier boundary bugs with kernel writes are historically high-risk and should not be auto-closed without source-level review. The evidence supports memory corruption and potential DoS. It does not prove arbitrary write, information disclosure, or reliable LPE. ## 5. One-sentence report phrase A verifier range mismatch in BPF conntrack kfunc wrappers can allow `opts.error` to be written outside the checked `opts__sz` range, creating a constrained kernel out-of-bounds write reachable by privileged XDP or TC BPF programs. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the issue is a BPF verifier boundary bypass with an out-of-bounds kernel write candidate. Even though typical access is capability gated and the payload is constrained, this class should be manually reviewed for adjacent object corruption, verifier assumptions, and possible reduced-capability deployment exposure. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Guard conntrack opts error writes [ Upstream Commit: dd74c80203842a21b2ebb9f70d1260d9aa20fa05 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dd74c80203842a21b2ebb9f70d1260d9aa20fa05 Changed files: net/netfilter/nf_conntrack_bpf.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=dd74c80203842a21b2ebb9f70d1260d9aa20fa05 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72423 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72423 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:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.8 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: 4 Paranoid ActionableScore: 6 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 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).