From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72433][MODERATE REGULAR] netfilter: nft_meta_bridge: fix NFT_META_BRI_IIFPVID stack leak [ Upstream Date: Sat, 15 Aug 2026 11:22:53 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72433 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: 2 X-AL-KERNEL-ActionableScore-Lower: 0 X-AL-KERNEL-Commit: c37a39b963034cc2d141baf46017614cb1fc275f List-Id: CVE: CVE-2026-72433 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: netfilter: nft_meta_bridge: fix NFT_META_BRI_IIFPVID stack leak [ Upstream Commit: c37a39b963034cc2d141baf46017614cb1fc275f Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c37a39b963034cc2d141baf46017614cb1fc275f Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72433 Analysis date: Sat, 15 Aug 2026 11:22:53 -0400 ActionableScore: 2 ActionableScore lower bound: 0 Actionable bucket: Ordinary Moderate / Low-like, but manual check required for stack leak exposure Manual review required: YES Summary: `NFT_META_BRI_IIFPVID can copy an uninitialized 16 bit stack value into an nftables register when br_vlan_get_pvid_rcu fails, causing a limited local kernel information leak that typically requires CAP_NET_ADMIN but may be relevant in delegated container or service environments.` ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72433 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72433 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-2026-72433 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:L/I:N/A:N';*CWE-457;*CWE-200;CWE-908;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '3.3';DESCR 'NFT_META_BRI_IIFPVID in nft_meta_bridge can store an uninitialized stack value because the return value from br_vlan_get_pvid_rcu is not checked before p_pvid is copied into an nftables register. This is an information disclosure bug rather than memory corruption because the visible primitive is an uninitialized 16 bit stack read, with no evidence of UAF, OOB write, or arbitrary write. For the CVSS the PR:L is used for the paranoid score because reliable exploitation may be possible in environments where an untrusted container, service account, or reduced capability root has delegated CAP_NET_ADMIN for nftables configuration. The issue is not directly network reachable as a standalone remote attack, although packets crossing a configured bridge can exercise the vulnerable rule after the ruleset exists. Impact is limited confidentiality exposure through kernel stack data and does not indicate integrity impact, availability impact, or privilege escalation by itself. YES REQUIRES MANUAL CHECK because this is a kernel stack leak and the practical impact depends on whether leaked register data can be exposed through a real nftables ruleset.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like, but manual check required for stack leak exposure (with actual score 1) SKIP CVE-2026-72433 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: c54c7c685494 YES NO NO unknown MAYBE SIMPLEFIX NETFILTER LEAK TEST DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=0 ## 1. ActionableScore * Conservative score: 0 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like, but manual check required for stack leak exposure**:: ## 2. Signal breakdown Conservative signals: * Confidentiality impact plausible: +1 The patch prevents an uninitialized 16 bit stack value in `p_pvid` from being stored into an nftables register. This is a limited kernel stack information disclosure primitive. * Common networking packet-processing path: +1 The affected code is in netfilter bridge nft meta evaluation, which is part of packet-path rule evaluation once a suitable ruleset exists. * Requires CAP_NET_ADMIN in typical deployments: -2 Creating or modifying the nftables bridge rule needed to exercise this path normally requires CAP_NET_ADMIN or equivalent administrative control. Conservative total: 0 Paranoid adjustment: * Privilege penalty relaxed from -2 to 0 In containerized or delegated-network-administration environments, CAP_NET_ADMIN may be available to a reduced-privilege root, service account, or container root that is not equivalent to full host root. * No memory corruption signal is added The primitive is an uninitialized stack read into an nft register, not UAF, OOB write, arbitrary write, refcount corruption, or type confusion. * No LPE signal is added The patch does not show attacker-controlled overwrite, object replacement, callback control, or a concrete privilege-escalation path. Paranoid total: 2 Call-site confidence: high. The changed function and the direct unsafe store into the nft register are visible in the provided patch. ## 3. Reachability analysis The bug is triggered through an nftables bridge meta expression using `NFT_META_BRI_IIFPVID`. A local actor normally needs CAP_NET_ADMIN to install the relevant nftables rule. After the rule exists, bridge traffic may exercise the expression, but this is not a standalone remote network attack because the attacker must first influence the ruleset or rely on a preexisting vulnerable rule. Namespaces and containers matter. If CAP_NET_ADMIN is delegated to an untrusted container or reduced-capability service, the practical PR can be closer to PR:L even though ordinary host deployments treat it as privileged administration. The path is not a default passive exposure. It depends on nftables bridge rules and bridge VLAN behavior. ## 4. Severity interpretation This behaves like a limited information disclosure issue, not an Important-class memory corruption bug. The realistic primitive is disclosure of a small uninitialized stack value into nftables evaluation state. There is no evidence of integrity impact, availability impact, UAF, OOB write, arbitrary write, or privilege escalation. The reason it should not be blindly auto-closed is that kernel stack leaks can sometimes become useful as helper leaks depending on whether the ruleset can expose or encode the leaked register value. ## 5. One-sentence report phrase `NFT_META_BRI_IIFPVID can copy an uninitialized 16 bit stack value into an nftables register when br_vlan_get_pvid_rcu fails, causing a limited local kernel information leak that typically requires CAP_NET_ADMIN but may be relevant in delegated container or service environments.` ## 6. Manual review recommendation MANUAL CHECK REQUIRED YES REQUIRES MANUAL CHECK because this is a kernel stack leak and the real impact depends on whether the leaked nft register value can be exposed, logged, encoded, or otherwise observed through a practical nftables ruleset. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfilter: nft_meta_bridge: fix NFT_META_BRI_IIFPVID stack leak [ Upstream Commit: c37a39b963034cc2d141baf46017614cb1fc275f Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c37a39b963034cc2d141baf46017614cb1fc275f Changed files: net/bridge/netfilter/nft_meta_bridge.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=c37a39b963034cc2d141baf46017614cb1fc275f ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72433 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72433 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:N/A:N The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N The Best / paranoid CVSS score: 3.3 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: 0 Paranoid ActionableScore: 2 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).