From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53070][MODERATE REGULAR] sctp: disable BH before calling udp_tunnel_xmit_skb() [ Upstream Date: Thu, 25 Jun 2026 15:17:45 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53070 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: 3 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 790093245e35040c2adb15f48970020425aa3f47 List-Id: CVE: CVE-2026-53070 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: sctp: disable BH before calling udp_tunnel_xmit_skb() [ Upstream Commit: 790093245e35040c2adb15f48970020425aa3f47 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=790093245e35040c2adb15f48970020425aa3f47 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53070 Analysis date: Thu, 25 Jun 2026 15:17:45 -0400 ActionableScore: 3 ActionableScore lower bound: 2 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: SCTP over UDP transmit may run udp_tunnel_xmit_skb() without BH disabled, allowing CPU migration to break per CPU recursion accounting and causing packet drops or severe SCTP throughput degradation on exposed SCTP UDP encapsulation deployments. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53070 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53070 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-53070 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;**CWE-400;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'SCTP over UDP transmit can call udp_tunnel_xmit_skb() or udp_tunnel6_xmit_skb() without bottom halves disabled. This can let execution move between CPUs while per CPU xmit recursion accounting is incremented and decremented, causing incorrect recursion level detection and packet drops in ip(6)_tunnel_xmit or __dev_queue_xmit. For the CVSS the PR:N is used for the paranoid score because a remote peer may trigger transmit on an exposed SCTP over UDP endpoint without local credentials. The issue is network reachable only when SCTP UDP encapsulation is enabled and usable by the attacker, which makes reliable triggering configuration dependent. Impact is denial of service through packet loss and degraded SCTP throughput, with no supported confidentiality or integrity impact from the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3) MAYBE OOB NETWORK HARDWARE LINUS TEST IPV6 PACKET DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 3 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown * Remote reachable / network-triggerable: +2 An exposed SCTP over UDP endpoint may be influenced by a remote peer to exercise this transmit path. * Availability impact realistic: +1 The demonstrated effect is incorrect recursion accounting and packet drops, with severe SCTP throughput degradation. * Common networking packet-processing path: +1, paranoid only This is in the networking transmit data path, but not a broad default TCP/IP path, so I count it only for the paranoid score. * Rare AND difficult-to-reach subsystem/configuration: -1 SCTP over UDP encapsulation must be enabled and usable. This is not a common default Internet-facing configuration. * No memory corruption: +0 The patch fixes BH/preemption context around per-CPU recursion accounting. It does not indicate UAF, OOB write, double-free, or controlled corruption. * No privilege escalation plausible: +0 The observed impact is packet loss / throughput degradation, not object lifetime corruption or privilege boundary bypass. ## 3. Reachability analysis A remote peer may trigger the affected path if SCTP over UDP encapsulation is enabled and the target participates in SCTP traffic over that UDP encapsulation. No local credentials are necessarily required for the paranoid interpretation, so remote PR:N is defensible for exposed deployments. However, the feature is configuration-dependent and not a common default public-facing service. Namespaces can make this easier to reproduce in test environments, but practical host impact depends on whether a real SCTP/UDP service is exposed. ## 4. Severity interpretation This behaves like a network-reachable DoS / packet-loss bug, not a memory-safety vulnerability. The realistic impact is service degradation or loss of SCTP over UDP throughput due to incorrect per-CPU xmit recursion accounting. There is no supported confidentiality or integrity impact from the patch context. It is not an Important-class candidate, but because it is potentially network-triggerable in enabled deployments, it should not be blindly auto-closed without checking exposure. ## 5. One-sentence report phrase SCTP over UDP transmit may run udp_tunnel_xmit_skb() without BH disabled, allowing CPU migration to break per CPU recursion accounting and causing packet drops or severe SCTP throughput degradation on exposed SCTP UDP encapsulation deployments. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: network reachability is plausible when SCTP over UDP encapsulation is enabled, but the bug is configuration-dependent and appears limited to availability impact without memory corruption or privilege escalation. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: sctp: disable BH before calling udp_tunnel_xmit_skb() [ Upstream Commit: 790093245e35040c2adb15f48970020425aa3f47 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=790093245e35040c2adb15f48970020425aa3f47 Changed files: net/sctp/ipv6.c net/sctp/protocol.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=790093245e35040c2adb15f48970020425aa3f47 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53070 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53070 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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.9 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: 2 Paranoid ActionableScore: 3 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).