From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53134][MODERATE 7.0] netfilter: nft_fib: fix stale stack leak via the OIFNAME register [ Upstream Date: Thu, 25 Jun 2026 05:02:02 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53134 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: 5 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 6744e49fe51bfba26522acc2d0e9703cb41d8e50 List-Id: CVE: CVE-2026-53134 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: netfilter: nft_fib: fix stale stack leak via the OIFNAME register [ Upstream Commit: 6744e49fe51bfba26522acc2d0e9703cb41d8e50 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6744e49fe51bfba26522acc2d0e9703cb41d8e50 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53134 Analysis date: Thu, 25 Jun 2026 05:02:02 -0400 ActionableScore: 5 ActionableScore lower bound: 2 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A stale stack disclosure in `nft_fib` can expose uninitialized `nft_regs` bytes to userspace when an OIFNAME or invalid PRESENT result writes less data than the declared register span, requiring nftables rule control and primarily causing confidentiality impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53134 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53134 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-2026-53134 MODERATE CHECK 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:N/A:N';*CWE-200;CWE-908;*CWE-457;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'nft_fib can leave stale bytes in the nft_regs stack area because the OIFNAME result reserves IFNAMSIZ bytes while some lookup fail and local return paths wrote only one 32 bit register. A later nftables expression that reads the full declared register span may expose uninitialized kernel stack data to userspace. For the CVSS the PR:L is used for the paranoid score because CAP_NET_ADMIN may be available to a local unprivileged user inside a user namespace or delegated network namespace, even though many production systems require administrator privileges. The issue is not directly network reachable because packet traffic alone cannot install the required nftables expression chain. Impact is confidentiality loss from kernel stack disclosure, with no write primitive and no direct denial of service indicated. YES REQUIRES MANUAL CHECK.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES REMOTE NETFILTER LEAK NETWORK IPV6 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown * Confidentiality impact plausible: +1 The bug can leak uninitialized kernel stack bytes from `nft_do_chain()` register storage to userspace through a downstream nftables expression. * Broad/default/common subsystem: +1 `nf_tables` is a common Linux firewall subsystem and is widely deployed. * Common packet-processing path: +1 The vulnerable expression is evaluated in the netfilter packet path once the ruleset is installed. * Local high-control kernel data-plane API: +1 nftables lets a user with rule-management privileges shape expressions, destination registers, result types, and downstream register consumers. * Requires CAP_NET_ADMIN in typical deployments: -2 Installing the malicious nftables rule normally requires `CAP_NET_ADMIN`. * Local unprivileged trigger in paranoid interpretation: +1 On systems with unprivileged user namespaces or delegated network namespaces, a local user may obtain `CAP_NET_ADMIN` inside a namespace and configure nftables there. No memory corruption, UAF, write primitive, reliable DoS, or privilege escalation primitive is shown by the patch. ## 3. Reachability analysis The bug is not directly network reachable. Remote packet traffic alone cannot install the required nftables rule chain or select the leaking register layout. A local actor with nftables control can configure `NFT_FIB_RESULT_OIFNAME` or invalid `NFTA_FIB_F_PRESENT` combinations and then use a downstream expression to read the stale register span. In normal host deployments this requires `CAP_NET_ADMIN`, but in environments with unprivileged user namespaces, containers, or delegated network administration, practical privileges may be closer to local unprivileged or low-privileged access. The subsystem is common, but the exploitability depends on ability to control nftables rules. ## 4. Severity interpretation This behaves like an actionable Moderate issue rather than a generic Low cleanup because it is a kernel stack information disclosure in a common packet-processing subsystem. It is not an Important-class memory corruption bug by itself: the patch shows stale stack bytes being read, not a UAF, OOB write, arbitrary write, callback corruption, or privilege escalation primitive. The realistic impact is confidentiality loss, potentially including kernel pointers or other stack-resident data useful for exploit development. ## 5. One-sentence report phrase A stale stack disclosure in `nft_fib` can expose uninitialized `nft_regs` bytes to userspace when an OIFNAME or invalid PRESENT result writes less data than the declared register span, requiring nftables rule control and primarily causing confidentiality impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Kernel stack disclosure in `nf_tables` should not be auto-closed, especially because namespace or container configurations may reduce the effective privilege requirement from host `CAP_NET_ADMIN` to a lower local attacker model. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfilter: nft_fib: fix stale stack leak via the OIFNAME register [ Upstream Commit: 6744e49fe51bfba26522acc2d0e9703cb41d8e50 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6744e49fe51bfba26522acc2d0e9703cb41d8e50 Changed files: net/ipv4/netfilter/nft_fib_ipv4.c net/ipv6/netfilter/nft_fib_ipv6.c net/netfilter/nft_fib.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=6744e49fe51bfba26522acc2d0e9703cb41d8e50 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53134 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53134 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:H/I:N/A:N 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: 2 Paranoid ActionableScore: 5 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).