From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46319][IMPORTANT] net/sched: act_ct: Only release RCU read lock after ct_ft [ Upstream Date: Mon, 06 Jul 2026 20:51:41 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46319 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: 7 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: ece578ca61e572df96cfc80456357ebfae0b4b9e List-Id: CVE: CVE-2026-46319 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: net/sched: act_ct: Only release RCU read lock after ct_ft [ Upstream Commit: ece578ca61e572df96cfc80456357ebfae0b4b9e Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ece578ca61e572df96cfc80456357ebfae0b4b9e Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46319 Analysis date: Mon, 06 Jul 2026 20:51:41 -0400 ActionableScore: 7 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A race in `net/sched act_ct` can free a `ct_ft` flow-table object after lookup but before its reference count is acquired, causing a use-after-free that may allow a local `CAP_NET_ADMIN` capable attacker to crash the kernel or potentially escalate privileges. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46319 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46319 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-2026-46319 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-362;CWE-667;BEST CVSS score: '7';DESCR 'A race in net sched act_ct can leave a ct_ft pointer unprotected after rhashtable lookup and before the reference count is acquired. If cleanup runs in that window, the flow table object can be removed and freed, and the later refcount operation can access freed memory. This is a use-after-free condition in kernel control plane code and it may allow local privilege escalation or a kernel crash. For the CVSS the PR:L is selected because reliable triggering requires local ability to configure tc act_ct or equivalent CAP_NET_ADMIN access, which can be available to a reduced capability root, container root, or service account rather than full host root. The issue is not directly network reachable and is triggered by local traffic control configuration activity. Impact is at least local denial of service and in worst case full confidentiality, integrity, and availability impact due to a race based UAF primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES REMOTE LOCK RACE UAF NETWORK LINUS KPANIC NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=6 ## 1. ActionableScore * Conservative score: 6 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Triggered signals: * Generic memory corruption, strong corruption primitive: +2 The patch fixes a real use-after-free where `ct_ft` can be freed before `refcount_inc_not_zero()` is executed. * Strong LPE plausibility: +2 The advisory explicitly states that the vulnerability can lead to privilege escalation, and the UAF involves a refcount operation on a freed kernel object, which is more concerning than a pure NULL dereference or crash-only bug. * Real lifetime corruption: +1 This is an RCU lifetime bug: lookup returns an object after the RCU read-side critical section has ended, leaving a stale pointer window before the reference is acquired. * Reliable kernel crash / strong DoS: +1 A UAF in this path can plausibly crash the kernel, even if privilege escalation is not achieved. * Broad/default/common subsystem exposure: +1 `net/sched` and `tc` actions are common kernel networking control-plane components, especially on container hosts and systems using traffic shaping or offload rules. Subtracted signals: * Hard or unreliable race / special timing required: -1 The report notes that the race window is very short and required an artificial `msleep(100)` to make triggering easier. * Requires CAP_NET_ADMIN or equivalent in typical deployments: -1 conservative Triggering typically requires the ability to configure `tc act_ct`. This is not ordinary unprivileged access, but it may be reachable by container root, delegated network administrators, or reduced-capability service accounts, so the full -2 root/admin penalty is not applied. Paranoid difference: * Paranoid score removes or weakens the privilege penalty because CAP_NET_ADMIN in a namespace or reduced-capability context is not equivalent to full host root, and the bug may cross a meaningful privilege boundary. ## 3. Reachability analysis The bug is triggered locally through traffic control configuration involving `act_ct`, not by ordinary incoming network packets alone. A realistic attacker needs the ability to create or modify `tc` actions, usually requiring `CAP_NET_ADMIN` in the relevant network namespace. Namespaces matter here. In typical host deployments this is privileged, but in containerized or delegated networking environments `CAP_NET_ADMIN` may be granted to a container root or service account that is not equivalent to full host root. That makes PR:L a defensible CVSS interpretation and prevents treating this as a fully admin-only non-issue. The vulnerable path is not directly remote network reachable. However, it is in a common networking subsystem and involves a real RCU/refcount lifetime bug in kernel memory management. Call-site confidence: high. The input includes the lookup path, the refcount acquisition point, the free path, and the patch that extends RCU protection across lookup and refcount acquisition. ## 4. Severity interpretation This behaves more like an Important-class kernel vulnerability than an ordinary Moderate issue. The realistic exploitability is limited by the short race window and the need for `tc act_ct` configuration privileges. However, the primitive is a real UAF on a refcounted kernel object, and the advisory explicitly states potential privilege escalation. The conservative view is Actionable Moderate / Important-candidate because the race is hard and no full exploit primitive is shown. The paranoid view reaches Strong Important candidate because refcount-after-free in a common kernel networking subsystem is historically dangerous and may be exploitable in reduced-privilege namespace scenarios. ## 5. One-sentence report phrase A race in `net/sched act_ct` can free a `ct_ft` flow-table object after lookup but before its reference count is acquired, causing a use-after-free that may allow a local `CAP_NET_ADMIN` capable attacker to crash the kernel or potentially escalate privileges. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This is a race-based UAF with an explicit privilege-escalation claim and a concrete RCU/refcount lifetime window. Even though the race is hard to trigger, it should not be auto-closed because namespace-delegated `CAP_NET_ADMIN` can make the practical privilege boundary weaker than full host root. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: act_ct: Only release RCU read lock after ct_ft [ Upstream Commit: ece578ca61e572df96cfc80456357ebfae0b4b9e Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ece578ca61e572df96cfc80456357ebfae0b4b9e Changed files: net/sched/act_ct.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=ece578ca61e572df96cfc80456357ebfae0b4b9e ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46319 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46319 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: Not available 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: 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: 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).