From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46321][MODERATE REGULAR] tun: free page on short-frame rejection in tun_xdp_one() [ Upstream Date: Tue, 09 Jun 2026 09:18:14 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46321 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: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 69863ff2720a0e9871f1a5710f2a33a94217fee0 List-Id: CVE: CVE-2026-46321 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: tun: free page on short-frame rejection in tun_xdp_one() [ Upstream Commit: 69863ff2720a0e9871f1a5710f2a33a94217fee0 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=69863ff2720a0e9871f1a5710f2a33a94217fee0 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46321 Analysis date: Tue, 09 Jun 2026 09:18:14 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Ordinary Moderate / Borderline resource exhaustion DoS Manual review required: NO Summary: A local process with access to TUN/TAP and vhost-net can repeatedly submit short vhost TX frames that leak page fragments in `tun_xdp_one()`, potentially exhausting host memory and causing an OOM panic. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46321 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46321 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-46321 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:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A page leak in the TUN/TAP vhost-net transmit path occurs because tun_xdp_one() returns -EINVAL for frames shorter than ETH_HLEN after vhost_net_build_xdp() allocated a page for the XDP buffer. The caller treats the batch as successfully consumed, so the page-frag chunk is not released and each malformed short frame can leak memory. For the CVSS the PR:L is used because a local process or service account with access to /dev/net/tun and /dev/vhost-net is needed to configure the TUN/TAP and vhost-net path and submit TX descriptors. The issue is not directly network reachable because the trigger is a local device and vhost control path rather than inbound network traffic. Impact is denial of service through host memory exhaustion and possible OOM panic, with no supported confidentiality or integrity impact and no supported privilege escalation path.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Borderline resource exhaustion DoS (with actual score 4) YES SIMPLEFIX LEAK ERRORPATH NETWORK HARDWARE INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Ordinary Moderate / Borderline resource exhaustion DoS**:: ## 2. Signal breakdown Triggered signals: * Local low-privileged trigger: +1 A local process with access to `/dev/net/tun` and `/dev/vhost-net` can trigger the leak through the TUN/TAP plus vhost-net TX path. This is not remote, but it may be reachable by VM or networking service accounts rather than full host root. * Reliable kernel crash / strong DoS: +1 The commit explicitly says repeated short frames can exhaust host memory and trigger an OOM panic. * Availability impact realistic: +1 This is not just a warning or minor leak. A tight submission loop can cause host-wide memory exhaustion. Paranoid-only signal: * Broad/common virtualization networking exposure: +1 TUN/TAP and vhost-net are common in virtualization and container/networking deployments. This does not make it remote, but it increases practical exposure in systems that delegate these devices to non-root service accounts. Not applied: * Remote reachable: +0 The trigger is a local device/vhost control path, not inbound network traffic. * Generic memory corruption: +0 The bug is a page reference leak/resource leak, not UAF, OOB write, double free, or type confusion. * Privilege escalation plausible: +0 No supported LPE primitive is visible. The impact is memory exhaustion. * Confidentiality/Integrity impact: +0 No leak of data and no write/corruption primitive is shown. * Requires full admin penalty: not fully applied Some deployments require elevated privileges or device permissions, but the relevant attacker may be a reduced-privilege VM or network service account with delegated access, not full host root. ## 3. Reachability analysis The bug is triggerable by a local process that can use `/dev/net/tun` and `/dev/vhost-net`, attach a TUN/TAP device as a vhost-net backend, and submit TX descriptors with payload shorter than `ETH_HLEN` after the virtio-net header. Ordinary remote packets do not directly reach this path. In typical deployments, creating or configuring TUN/TAP may require `CAP_NET_ADMIN` or preconfigured persistent devices, while vhost-net access is commonly granted to virtualization stacks such as QEMU. Containers or service accounts with delegated network or vhost access may reduce the practical privilege requirement from host-root to PR:L-like access. The path is common in virtualization networking, but not universally exposed to untrusted local users by default. ## 4. Severity interpretation This behaves like a resource-exhaustion DoS, not an Important-class memory corruption issue. The realistic impact is host memory exhaustion and possible OOM panic after repeated local submissions. There is no evidence of UAF reuse, attacker-controlled overwrite, object confusion, information disclosure, or privilege escalation. The conservative result is ordinary Moderate. The paranoid result reaches borderline Actionable Moderate only because the DoS can be host-wide and the affected TUN/vhost-net path is common in virtualization environments. ## 5. One-sentence report phrase A local process with access to TUN/TAP and vhost-net can repeatedly submit short vhost TX frames that leak page fragments in `tun_xdp_one()`, potentially exhausting host memory and causing an OOM panic. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED This is a clear resource leak with strong DoS potential but no demonstrated memory corruption, confidentiality impact, integrity impact, or privilege-escalation primitive. Normal patch tracking is appropriate unless the environment delegates `/dev/net/tun` and `/dev/vhost-net` broadly to untrusted tenants. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: tun: free page on short-frame rejection in tun_xdp_one() [ Upstream Commit: 69863ff2720a0e9871f1a5710f2a33a94217fee0 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=69863ff2720a0e9871f1a5710f2a33a94217fee0 Changed files: drivers/net/tun.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=69863ff2720a0e9871f1a5710f2a33a94217fee0 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46321 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46321 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:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H 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: 3 Paranoid ActionableScore: 4 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).