From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80681][MODERATE 7.0] vxlan: re-fetch eth header after route_shortcircuit() Date: Fri, 28 Aug 2026 04:31:18 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80681 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: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 6375093eb45cd7d89f1945f939eeae3b29d79f56 List-Id: CVE: CVE-2026-80681 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: vxlan: re-fetch eth header after route_shortcircuit() Commit: 6375093eb45cd7d89f1945f939eeae3b29d79f56 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6375093eb45cd7d89f1945f939eeae3b29d79f56 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80681 Analysis date: Fri, 28 Aug 2026 04:31:18 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A use-after-free in the VXLAN transmit path occurs because vxlan_xmit() reuses a cached Ethernet header pointer after route_shortcircuit() may reallocate skb head, allowing network-adjacent VXLAN traffic to trigger a stale eth h_dest dereference and cause at least a kernel crash (DoS). ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80681 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80681 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-2026-80681 MODERATE CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-825;*CWE-664;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A use-after-free in the VXLAN transmit path can occur because vxlan_xmit caches the Ethernet header pointer before route_shortcircuit(). route_shortcircuit() may call pskb_may_pull(), which can reallocate skb head and leave the cached eth pointer stale. A packet that reaches the affected VXLAN route shortcircuit path can then cause a dereference of eth h_dest from freed memory, leading at least to kernel crash or incorrect forwarding behavior. For the CVSS the PR:N because the attacker does not need a local account if they can inject traffic into the relevant VXLAN or attached tenant network path. The attack is best modeled as AV:A because VXLAN deployments are usually limited to adjacent overlay, cloud, or data center networks rather than the public Internet. Impact is at least denial of service, with limited confidentiality or integrity impact possible in the paranoid interpretation due to a stale UAF read that influences MAC lookup.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES UAF NETWORK SKB LINUS IPV6 KPANIC KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2. The affected path is VXLAN packet transmission and can be reached by traffic entering the relevant VXLAN or tenant overlay path. * Memory corruption, weak/indirect corruption candidate: +1. This is a stale pointer use-after-free read of a cached Ethernet header pointer, but the patch does not show attacker-controlled reclaim, overwrite, callback control, or type confusion. * Real lifetime corruption: +1. pskb_may_pull() may reallocate skb head, leaving the cached eth pointer referring to freed memory. * Reliable kernel crash / strong DoS: +1. Dereferencing a freed Ethernet header pointer in the transmit path can plausibly crash the kernel. * Common networking packet-processing path: +1. VXLAN is a commonly deployed overlay networking datapath in cloud and data-center environments. * Hard or special triggering conditions: -1. Triggering requires the route_shortcircuit() path and an skb layout where pskb_may_pull() reallocates skb head. Paranoid additional signals: * Confidentiality impact plausible: +1. Limited information exposure is theoretically possible if behavior depending on freed header bytes is externally observable, but no direct disclosure primitive is shown. * Integrity impact plausible: +1. eth h_dest from stale memory may influence MAC lookup or forwarding decisions, giving a limited integrity concern in the paranoid interpretation. Not awarded: * Strong LPE plausibility: +0. No attacker-controlled reclaim, writable stale object access, function pointer control, type confusion, or refcount takeover is shown. * Strong corruption primitive: +0. The demonstrated primitive is stale read/dereference, not an arbitrary write or controlled overwrite. * Availability impact realistic: +0 additional. Crash/DoS was already counted and should not be double-counted. ## 3. Reachability analysis The most realistic attacker is a network-adjacent actor that can inject traffic into the affected VXLAN or tenant overlay network. This should not be modeled as general Internet remote exposure in most deployments, because VXLAN is normally used inside data-center, virtualization, cloud, or overlay networks. For the CVSS the PR:N because the attacker does not need a local account on the victim host if they can send packets into the relevant VXLAN path. Creating or configuring the VXLAN interface requires administrative privileges, but triggering the bug can be packet-driven once the vulnerable configuration exists. Namespaces and containers matter mainly for deployment. A tenant or container workload may be able to generate traffic that reaches the VXLAN datapath, but the vulnerable route_shortcircuit configuration is typically host-controlled. Call-site confidence: high. The provided diff shows the stale eth pointer being used immediately after route_shortcircuit() in vxlan_xmit(). ## 4. Severity interpretation This is stronger than an ordinary Moderate because it is a real lifetime bug in a networking datapath and the trigger can be packet-driven in affected VXLAN deployments. It is not a clear Important LPE case because the patch only demonstrates stale pointer dereference/read, not controlled reuse or overwrite. The conservative interpretation is Actionable Moderate. The paranoid interpretation reaches Strong Important candidate because it combines network-adjacent reachability, UAF lifetime corruption, likely DoS, and limited possible C/I impact from stale header data influencing forwarding behavior. ## 5. One-sentence report phrase A use-after-free in the VXLAN transmit path occurs because vxlan_xmit() reuses a cached Ethernet header pointer after route_shortcircuit() may reallocate skb head, allowing network-adjacent VXLAN traffic to trigger a stale eth h_dest dereference and cause at least a kernel crash (DoS). ## 6. Manual review recommendation MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK. Reason: this is a real UAF in a networking packet path with network-adjacent trigger conditions. The available patch supports DoS strongly and limited C/I concern defensibly, but does not prove a practical privilege escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: vxlan: re-fetch eth header after route_shortcircuit() Commit: 6375093eb45cd7d89f1945f939eeae3b29d79f56 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6375093eb45cd7d89f1945f939eeae3b29d79f56 Commit description: Before route_shortcircuit(), the eth header pointer is cached from eth_hdr(skb). Inside route_shortcircuit(), pskb_may_pull() can be called, which may reallocate skb->head. In this case, returning to vxlan_xmit() leaves the cached eth pointer pointing to freed memory, leading to a use-after-free when dereferencing eth->h_dest. Fix this by updating eth = eth_hdr(skb) after calling route_shortcircuit(). Fixes: ae88408 ("VXLAN: Allow L2 redirection with L3 switching") Cc: stable@vger.kernel.org Signed-off-by: Eric Dumazet Reviewed-by: Vadim Fedorenko Link: https://patch.msgid.link/20260723144249.759100-2-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: drivers/net/vxlan/vxlan_core.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=6375093eb45cd7d89f1945f939eeae3b29d79f56 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80681 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80681 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:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 6.4 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: 5 Paranoid ActionableScore: 7 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).