From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74744][IMPORTANT] ipvlan: inherit needed_headroom and needed_tailroom from phy_dev [ Upstream Date: Wed, 26 Aug 2026 14:03:02 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74744 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 8 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: af602c4d0ee548da18e2409b4b4da1079625a372 List-Id: CVE: CVE-2026-74744 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: ipvlan: inherit needed_headroom and needed_tailroom from phy_dev [ Upstream Commit: af602c4d0ee548da18e2409b4b4da1079625a372 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af602c4d0ee548da18e2409b4b4da1079625a372 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74744 Analysis date: Wed, 26 Aug 2026 14:03:02 -0400 ActionableScore: 8 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: ipvlan devices failed to inherit lower-device headroom and tailroom requirements, allowing traffic through certain stacked network configurations to trigger skb underflow or KASAN slab-use-after-free crashes, with local DoS confirmed and memory-corruption impact requiring manual review. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74744 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74744 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: IMPORTANT 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-2026-74744 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-787;CWE-119;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'ipvlan devices did not inherit needed_headroom and needed_tailroom from the underlying physical or stacked lower device. When the lower path needs extra space for headers or trailers, upper layers may allocate skb buffers with insufficient reserve, and later header prepend or trailer append operations can hit skb headroom underflow or KASAN slab use after free conditions. For the CVSS the PR:L is used because reliable triggering generally requires a local process or tenant workload able to send traffic through an already configured ipvlan device, while creating the ipvlan and lower stack usually requires administrator setup. The issue is not treated as directly Internet reachable, although traffic through the affected ipvlan path can be network influenced in container or virtual networking deployments. Impact is at least local denial of service via kernel crash, and in the paranoid case may include confidentiality or integrity impact because the bug class includes skb memory corruption and a reported slab use after free.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) YES OOB DANGER UAF NETWORK SKB KERNEL_PANIC_PLUS_UAF HARDWARE SYZBOT KPANIC PACKET NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ## 1. ActionableScore ActionableScore=8 ActionableScoreLower=6 * Conservative score: 6 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1. A local workload can plausibly trigger traffic through an already configured ipvlan device. * Generic memory corruption: +2. The description explicitly mentions skb headroom underflows and KASAN slab-use-after-free crashes. * Memory layout invariant restoration: +1. The patch restores consistency between lower-device headroom/tailroom requirements and upper ipvlan skb allocation assumptions. * Real lifetime corruption: +1. Reported KASAN slab-use-after-free indicates a real lifetime or stale memory access condition, not just bookkeeping. * Reliable kernel crash / strong DoS: +1. The commit describes KASAN crashes in packet header or trailer handling paths. * Common networking packet-processing path: +1. ipvlan is not universal, but this is still an skb transmit/stacked-netdev packet path. * Special configuration required: -1. Reliable triggering depends on ipvlan over a lower device needing extra headroom or tailroom, such as macsec, IPsec, WireGuard, tunnels, or veth rx headroom. Paranoid additional signals: * Weak LPE concern: +1. The UAF/headroom-underflow class is security-relevant, but no attacker-controlled reclaim, callback control, or arbitrary write primitive is shown. * Integrity impact plausible: +1. skb memory corruption can plausibly affect kernel/network state beyond a clean crash, so this deserves manual review. Not counted: * Remote reachable: +0. This is network-influenced, but not directly Internet-reachable in the normal CVE sense. * Strong LPE plausibility: +0. No demonstrated reclaim, object replacement, type confusion, or controlled overwrite is shown. * Confidentiality impact: +0 for ActionableScore. It remains a paranoid CVSS consideration, but no concrete leak path is shown. ## 3. Reachability analysis The most realistic trigger is a local process, container workload, or tenant workload sending packets through an already configured ipvlan interface whose lower device requires nonzero needed_headroom or needed_tailroom. Creating the ipvlan and lower stacked configuration usually requires CAP_NET_ADMIN, but once the device exists, ordinary traffic generation may be enough to exercise the vulnerable path. Namespaces and container networking can therefore reduce practical privilege requirements if ipvlan devices are delegated to containers or tenant workloads. The path is not default-enabled on all systems, but ipvlan and stacked virtual or encrypted network devices are common enough that this should not be treated as obscure hardware-only exposure. Call-site confidence: medium-high. The patch is small, but the commit message identifies concrete downstream users, dev_hard_header(), ipvlan_hard_header(), and lower-device tailroom append paths. ## 4. Severity interpretation This is stronger than an ordinary Moderate because the failure mode is not just validation failure or resource exhaustion. The bug affects skb buffer sizing invariants and has reported KASAN slab-use-after-free crashes. Realistic evidence supports local DoS with special network configuration. Theoretical impact may extend to integrity or privilege escalation, but the patch does not show a controlled corruption primitive. Therefore the conservative result is Actionable Moderate, while the paranoid result is a Strong Important candidate requiring manual review. ## 5. One-sentence report phrase ipvlan devices failed to inherit lower-device headroom and tailroom requirements, allowing traffic through certain stacked network configurations to trigger skb underflow or KASAN slab-use-after-free crashes, with local DoS confirmed and memory-corruption impact requiring manual review. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is skb memory corruption with a reported KASAN slab-use-after-free in a network packet path. Even though practical exploitation likely requires a specific ipvlan/lower-device configuration and no strong LPE primitive is demonstrated, the bug class is too security-relevant to auto-close. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ipvlan: inherit needed_headroom and needed_tailroom from phy_dev [ Upstream Commit: af602c4d0ee548da18e2409b4b4da1079625a372 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af602c4d0ee548da18e2409b4b4da1079625a372 Changed files: drivers/net/ipvlan/ipvlan_main.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=af602c4d0ee548da18e2409b4b4da1079625a372 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74744 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74744 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:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7 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: 6 Paranoid ActionableScore: 8 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: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT 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).