From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-68299][MODERATE 7.0] vmxnet3: fix BUG_ON in vmxnet3_get_hdr_len() for Geneve packets [ Upstream Date: Mon, 10 Aug 2026 18:54:06 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-68299 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 667b6e52048eaf4dbcf1707ed87ffd44abb9cb38 List-Id: CVE: CVE-2026-68299 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: vmxnet3: fix BUG_ON in vmxnet3_get_hdr_len() for Geneve packets [ Upstream Commit: 667b6e52048eaf4dbcf1707ed87ffd44abb9cb38 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=667b6e52048eaf4dbcf1707ed87ffd44abb9cb38 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68299 Analysis date: Mon, 10 Aug 2026 18:54:06 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A reachable BUG_ON in vmxnet3 header parsing can be triggered by Geneve packet metadata that describes inner headers while the driver validates outer headers, allowing a network-adjacent attacker to crash an affected VMware Linux guest. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68299 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68299 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-2026-68299 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-617;*CWE-20;CWE-754;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A reachable BUG_ON in vmxnet3_get_hdr_len() can be hit when a Geneve-encapsulated packet causes the vmxnet3 completion descriptor to describe the inner header while the driver still validates the outer header. The outer Geneve header uses UDP, so the driver can wrongly expect TCP or the wrong IP version and crash the guest kernel. For the CVSS the PR:N because an attacker does not need local code execution or an account on the guest if crafted Geneve traffic can reach the vmxnet3 interface. The issue is network reachable in deployments where Geneve or similar encapsulated traffic is accepted by the affected VM network path. Impact is denial of service via kernel crash only. No concrete memory corruption primitive is indicated by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) YES SIMPLEFIX NETWORK HARDWARE LINUS IPV6 KPANIC PACKET KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: **4** * Paranoid score: **5** * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative scoring: * **Firmware or device mediated external influence: +1** The crash depends on vmxnet3 completion descriptor metadata generated by the virtual NIC for Geneve packets, not purely on a local syscall path. * **Reliable kernel crash / strong DoS: +1** The patch converts reachable `BUG_ON()` checks into defensive `return 0` paths. The described failure mode is a guest kernel crash. * **Common packet processing path: +1** The affected code is in the receive or header parsing path of a network driver. * **Broad/common deployment exposure: +1** vmxnet3 is commonly used in VMware virtualized Linux guests. Paranoid scoring difference: * **Remote reachable / network-triggerable: +2 instead of +1** If crafted Geneve traffic can reach the affected vmxnet3 interface, the issue becomes packet-triggerable without local code execution in the guest. Not counted: * **No generic memory corruption: +0** The patch shows reachable assertions and defensive validation, not UAF, OOB write, double free, type confusion, or arbitrary write. * **No privilege escalation plausible: +0** There is no concrete primitive beyond guest kernel crash. * **No confidentiality or integrity impact: +0** The evidence supports DoS only. ## 3. Reachability analysis An attacker can plausibly trigger the bug by sending Geneve-encapsulated traffic that causes vmxnet3 descriptor metadata to describe the inner header while the driver validates the outer header. No local account in the guest is required if the packet can reach the VM network path. Namespaces and containers are not central to the trigger because this is a network receive path in the guest kernel. The path is deployment dependent. It requires a Linux guest using the vmxnet3 driver and a network where Geneve or similar encapsulated packets can be delivered to the VM. This is more realistic in VMware, virtualized data-center, overlay-network, or tenant-network environments than on a generic public Internet host. ## 4. Severity interpretation This behaves as an **Actionable Moderate** issue rather than a Strong Important vulnerability. The realistic impact is a packet-triggered guest kernel DoS via reachable `BUG_ON()`. The theoretical memory corruption potential is low because the patch does not show stale lifetime, overwrite, object confusion, or attacker-controlled memory reuse. Manual triage is still warranted because the bug is in a network receive path and practical severity depends heavily on whether affected vmxnet3 guests can receive Geneve traffic from untrusted or tenant-controlled networks. ## 5. One-sentence report phrase A reachable BUG_ON in vmxnet3 header parsing can be triggered by Geneve packet metadata that describes inner headers while the driver validates outer headers, allowing a network-adjacent attacker to crash an affected VMware Linux guest. ## 6. Manual review recommendation **MANUAL CHECK REQUIRED** Reason: the issue is DoS-only, but it is in a network packet receive path and may be triggerable without guest-local privileges in realistic VMware or overlay-network deployments. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: vmxnet3: fix BUG_ON in vmxnet3_get_hdr_len() for Geneve packets [ Upstream Commit: 667b6e52048eaf4dbcf1707ed87ffd44abb9cb38 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=667b6e52048eaf4dbcf1707ed87ffd44abb9cb38 Changed files: drivers/net/vmxnet3/vmxnet3_drv.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=667b6e52048eaf4dbcf1707ed87ffd44abb9cb38 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68299 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68299 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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 7.5 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: 4 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: YES 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).