From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74669][IMPORTANT] ipvs: clear IPv4 options after rebasing tunnel ICMP errors Date: Sat, 22 Aug 2026 13:21:42 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74669 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: 8 X-AL-KERNEL-ActionableScore-Lower: 7 X-AL-KERNEL-Commit: 79ffa99202c944467e28b13b513bf2998732edff List-Id: CVE: CVE-2026-74669 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: ipvs: clear IPv4 options after rebasing tunnel ICMP errors Commit: 79ffa99202c944467e28b13b513bf2998732edff Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=79ffa99202c944467e28b13b513bf2998732edff Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74669 Analysis date: Sat, 22 Aug 2026 13:21:42 -0400 ActionableScore: 8 ActionableScore lower bound: 7 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A network-reachable IPVS tunnel ICMP handling bug can leave stale IPv4 option metadata after skb rebasing, causing `__ip_options_echo()` to perform a stack out-of-bounds write in `__icmp_send()`, with realistic DoS impact and possible higher memory-corruption risk. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74669 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74669 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-2026-74669 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-121;*CWE-664;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'IPVS can rebase an skb from an outer ICMP packet to the quoted original request while leaving stale IPv4 option metadata in IPCB(skb). A crafted outer IPv4 header with a timestamp option can make the stale option offset point into the quoted transport header, so __ip_options_echo() may treat attacker influenced data as an option length and write past fixed size option storage on the __icmp_send() stack. For the CVSS the PR:N is used because a remote sender does not need local privileges on the target when the affected IPVS tunnel ICMP path is reachable. The issue is network reachable but requires a specific IPVS tunnel configuration and crafted ICMP error handling, so AC:H is appropriate. Impact is at least denial of service and the stack out-of-bounds write gives a plausible memory corruption path, so manual review is required for confidentiality, integrity, and privilege escalation risk.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) SKIP CVE-2026-74669 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE WRITE OOB SIMPLEFIX NETFILTER SKB KPANIC PACKET - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=7 ## 1. ActionableScore * Conservative score: 7 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2 The affected path handles ICMP errors for IPVS tunnel traffic and can be influenced by network packets when the IPVS tunnel ICMP path is reachable. * Memory corruption, Strong corruption primitive: +2 The commit explicitly describes a stack out-of-bounds write in `__icmp_send()` via `__ip_options_echo()` copying into fixed-size option storage. * Reliable kernel crash / strong DoS: +1 A stack OOB write in the ICMP response path is a credible kernel crash condition. * Common networking packet-processing path: +1 This is in netfilter/IPVS packet handling, not a purely local control-plane ioctl or rare debug interface. * Confidentiality impact plausible: +1 Conservative C impact is not proven, but stack memory corruption can plausibly affect sensitive kernel state. * Integrity impact plausible: +1 Stack OOB write can plausibly corrupt control or data state, even if reliable control is not demonstrated. Negative signals: * Rare AND difficult-to-reach subsystem/configuration: -1 Triggering depends on IPVS tunnel behavior, ICMP error handling, and crafted IPv4 options. This is not a default Internet-exposed path on most systems. Paranoid additional signal: * Weak LPE / control-flow concern: +1 The primitive is a network-reachable stack OOB write. The patch does not prove controlled code execution, but this class deserves manual review for privilege escalation or remote code execution feasibility. ## 3. Reachability analysis A remote sender may trigger the bug if the target uses the affected IPVS tunnel ICMP path and accepts crafted ICMP error traffic with IPv4 options. No local account is required on the victim, so practical PR is none for exposed deployments. The path is configuration-dependent. IPVS and the relevant tunnel/passive PMTUD handling must be in use, and filtering may block the required ICMP traffic. Containers and namespaces can matter if IPVS is configured inside a network namespace, but the main risk is to the kernel handling the packet path. Call-site confidence: high. The commit message directly identifies the stale `IPCB(skb)->opt` metadata, the rebase in `ip_vs_in_icmp()`, the later `icmp_send()` path, and the stack OOB write in `__ip_options_echo()`. ## 4. Severity interpretation This behaves more like an Important-class candidate than an ordinary Moderate issue. The realistic demonstrated impact is at least remote DoS through kernel memory corruption. The theoretical risk is higher because the primitive is a stack out-of-bounds write in a network packet-processing path, but reliable exploitation beyond crash is not demonstrated by the patch alone. The configuration requirements justify avoiding a Critical-like classification, but the memory corruption primitive and remote trigger make this clearly unsuitable for auto-close. ## 5. One-sentence report phrase A network-reachable IPVS tunnel ICMP handling bug can leave stale IPv4 option metadata after skb rebasing, causing `__ip_options_echo()` to perform a stack out-of-bounds write in `__icmp_send()`, with realistic DoS impact and possible higher memory-corruption risk. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This is a remote packet-processing stack OOB write, not a DoS-only validation bug. Manual analysis is needed to determine attacker control over the copied length/data, stack layout impact, and whether exploitation can exceed kernel crash. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ipvs: clear IPv4 options after rebasing tunnel ICMP errors Commit: 79ffa99202c944467e28b13b513bf2998732edff Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=79ffa99202c944467e28b13b513bf2998732edff Commit description: ip_vs_in_icmp() rebases an skb from the outer ICMP packet to the quoted original request before passing it to icmp_send(). However, IPCB(skb)->opt still describes the outer IPv4 header. A timestamp option in the outer header can therefore leave an offset that points into the quoted transport header after the rebase. __ip_options_echo() treats a byte at that stale location as the option length and copies it into the fixed-size option storage on the __icmp_send() stack, causing a stack out-of-bounds write. Clear the stale option metadata after resetting the network header. Keep the remaining control block fields, including the ingress interface used by the ICMP response path. Fixes: f2edb9f ("ipvs: implement passive PMTUD for IPIP packets") Cc: stable@vger.kernel.org Assisted-by: Codex:gpt-5.6-sol Codex:gpt-5.5-cyber Signed-off-by: Kyle Zeng Co-developed-by: David Lee Signed-off-by: David Lee Acked-by: Julian Anastasov Signed-off-by: Pablo Neira Ayuso Signed-off-by: Greg Kroah-Hartman Changed files: net/netfilter/ipvs/ip_vs_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=79ffa99202c944467e28b13b513bf2998732edff ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74669 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74669 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:L/I:L/A:H The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 8.1 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: 7 Paranoid ActionableScore: 8 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).