From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53080][LOW] net/sched: cls_fw: fix NULL dereference of "old" filters before change() [ Upstream Date: Thu, 25 Jun 2026 14:07:32 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53080 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: 0 X-AL-KERNEL-Commit: a719275da488835e987d28effc04679b4aace3a0 List-Id: CVE: CVE-2026-53080 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: net/sched: cls_fw: fix NULL dereference of "old" filters before change() [ Upstream Commit: a719275da488835e987d28effc04679b4aace3a0 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a719275da488835e987d28effc04679b4aace3a0 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53080 Analysis date: Thu, 25 Jun 2026 14:07:32 -0400 ActionableScore: 2 ActionableScore lower bound: 0 Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: A local TC configuration race can briefly expose an invalid old-style `cls_fw` filter on a shared block, allowing packet classification to dereference a NULL qdisc pointer and crash the kernel. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53080 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53080 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: LOW 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-2026-53080 LOW 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-476;CWE-362;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'cls_fw old style classification can run on a filter that was published to a shared TC block before its change validation finishes. In that transient state, fw_classify can reach the old method path and dereference q handle when q is NULL, causing a kernel NULL pointer dereference and denial of service. For the CVSS the PR:L value is used for the paranoid score because reliable triggering requires a local process with traffic control administration capability such as CAP_NET_ADMIN or an equivalent delegated network administration context. The issue is not directly network reachable because packet traffic only triggers the dereference after a local control plane operation has installed the problematic filter state. Impact is denial of service via kernel crash. There is no clear evidence of a UAF, OOB access, information leak, or arbitrary write primitive in this patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1) SKIP CVE-2026-53080 SKIP The Fixes patch not applied yet, so unlikely that actual: faeea8bbf6e958bf3c00cb08263109661975987c YES NO NO unknown MAYBE REMOTE DANGER NULLPTR NETWORK SKB KERNEL_PANIC_PLUS_UAF HARDWARE LINUS QDISC PACKET DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=0 ## 1. ActionableScore * Conservative score: 0 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: ## 2. Signal breakdown * Reliable kernel crash / strong DoS: +1. The patch and trace show a NULL pointer dereference of `q->handle` in `fw_classify()`. * Local unprivileged trigger, paranoid only: +1. In environments with unprivileged user namespaces and delegated `CAP_NET_ADMIN` inside a network namespace, a local user may be able to configure the needed TC objects. * Requires admin/root/CAP_NET_ADMIN in typical deployments: -2 conservative. Creating qdiscs, shared TC blocks, and filters normally requires `CAP_NET_ADMIN`. * Hard or unreliable race / special timing required: -1 conservative. The invalid old-style filter must classify packets during its short lifetime before validation destroys it. * No generic memory corruption: +0. The demonstrated primitive is a NULL pointer dereference, not UAF, OOB write, double free, arbitrary write, or object reclaim. * No C/I impact counted. The patch does not show a confidentiality leak or integrity write primitive. * No remote/network-triggerable score. Packets only hit the bug after local TC control-plane setup. ## 3. Reachability analysis The realistic trigger is local TC configuration plus packet generation. In normal host deployments this requires `CAP_NET_ADMIN`, so the conservative score is very low. In container or namespace setups where an untrusted user can obtain `CAP_NET_ADMIN` in a network namespace, the practical privilege requirement may be lower, but the issue still remains a local control-plane-triggered NULL dereference. The affected path is not default-active. It requires `cls_fw`, shared TC blocks, and the old-style classification path. ## 4. Severity interpretation This behaves like an ordinary Moderate or Low-like kernel DoS, not an Important-class vulnerability. The theoretical risk is limited because the primitive is a NULL dereference of a missing qdisc pointer. There is no supported evidence of UAF, reclaim control, OOB write, information disclosure, arbitrary write, or privilege escalation. ## 5. One-sentence report phrase A local TC configuration race can briefly expose an invalid old-style `cls_fw` filter on a shared block, allowing packet classification to dereference a NULL qdisc pointer and crash the kernel. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED This can be auto-closed for practical triage unless your environment allows untrusted users to create network namespaces with `CAP_NET_ADMIN` and load or use `cls_fw`; even then, the expected impact is DoS only. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: cls_fw: fix NULL dereference of "old" filters before change() [ Upstream Commit: a719275da488835e987d28effc04679b4aace3a0 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a719275da488835e987d28effc04679b4aace3a0 Changed files: include/net/pkt_cls.h net/sched/cls_fw.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=a719275da488835e987d28effc04679b4aace3a0 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53080 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53080 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: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: 0 Paranoid ActionableScore: 2 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).