From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74662][IMPORTANT] inet: frags: publish queues before arming timer Date: Sat, 22 Aug 2026 15:56:55 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74662 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: 5 X-AL-KERNEL-Commit: 9f904dd3e455750e5d4ec9b2f134835811b85a2f List-Id: CVE: CVE-2026-74662 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: inet: frags: publish queues before arming timer Commit: 9f904dd3e455750e5d4ec9b2f134835811b85a2f Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9f904dd3e455750e5d4ec9b2f134835811b85a2f Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74662 Analysis date: Sat, 22 Aug 2026 15:56:55 -0400 ActionableScore: 8 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A race in inet fragment queue creation can arm the timer before rhashtable publication, allowing immediate timer expiry with zero or negative fragment timeout to leave a stale hash node and create a network-triggerable DoS or UAF candidate. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74662 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74662 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-2026-74662 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-362;*CWE-416;*CWE-672;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.1';DESCR 'inet fragment queue creation arms a timer before the queue is visible in the rhashtable. If the namespace fragment timeout is zero or negative, the timer can expire first and mark the queue complete, drop the anticipated hash reference, and leave a stale hash node after creation continues. This is a race and stale reference condition in the IP fragment reassembly path and can become a use after free candidate when later lookups or cleanup traverse the stale node. For the CVSS the PR:N is used for the paranoid network scenario because once the target namespace has this timeout setting, a remote sender can trigger queue creation with fragmented IP traffic without credentials. The issue is network reachable under that vulnerable configuration, but exploitation is configuration dependent and likely requires non default fragment timeout settings. Impact is at least denial of service via kernel crash. In the worst still defensible case, stale hash references may allow broader memory corruption impact, so manual review is recommended.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES REMOTE LOCK SIMPLEFIX NETWORK TIMER LINUS KPANIC NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown ### Conservative score signals * Remote reachable / network-triggerable: +2 IP fragment reassembly is reachable through fragmented network traffic if the affected namespace has a zero or negative fragment timeout. * Memory corruption, weak/indirect corruption candidate: +1 The stale rhashtable node and unbalanced hash reference create a stale lifetime condition. The patch supports a UAF candidate, but does not show attacker-controlled reclaim, overwrite, type confusion, or callback control. * Real lifetime corruption: +1 The bug is explicitly about publishing a completed fragment queue after the timer has dropped the anticipated hash reference, leaving stale lifetime state. * Reliable kernel crash / strong DoS: +1 Later lookup or cleanup of the stale hash node can plausibly crash the kernel. * Common networking core path or packet-processing path: +1 inet fragment queues are part of common IPv4/IPv6 packet reassembly infrastructure. * Configuration / timing constraint: -1 Practical remote triggering depends on a zero or negative fragment timeout, which is a special runtime condition and likely non-default. Conservative total: 5 ### Paranoid score signals * Remote reachable / network-triggerable: +2 Once the vulnerable timeout configuration exists, a remote sender can create fragment queues with fragmented traffic without credentials. * Memory corruption, strong corruption primitive: +2 For paranoid triage, the stale rhashtable node after reference imbalance is treated as a stronger UAF style lifetime corruption candidate in a network packet path. * Real lifetime corruption: +1 The root cause is reference lifetime imbalance between timer expiry, rhashtable publication, and final queue release. * Reliable kernel crash / strong DoS: +1 A stale published node can lead to kernel crash during later traversal or cleanup. * Common networking core path or packet-processing path: +1 The affected logic is in inet fragment reassembly, not a rare driver-only path. * Confidentiality impact plausible: +1 Only for paranoid scoring, stale object traversal could theoretically expose broader memory corruption consequences. * Integrity impact plausible: +1 Only for paranoid scoring, a UAF-class stale node in a network path warrants manual review for possible corruption beyond DoS. * Configuration / timing constraint: -1 The zero or negative timeout condition remains an important practical limiter. Paranoid total: 8 ## 3. Reachability analysis A remote attacker can plausibly trigger the affected path by sending fragmented IP traffic, but only if the target namespace fragment timeout is zero or negative. Setting that timeout likely requires local administrative control such as CAP_NET_ADMIN, so the strongest network scenario depends on a preexisting vulnerable configuration rather than attacker-controlled configuration. Namespaces matter because fragment timeout is namespace-scoped. A container or delegated network namespace with CAP_NET_ADMIN could potentially create the vulnerable condition locally, while an external attacker benefits only if such a namespace or host configuration already exists. The affected code is in common inet fragment reassembly infrastructure. The trigger condition is not default-like, but the subsystem itself is central networking code. Call-site confidence: medium, because the patch and commit clearly describe the timer, rhashtable publication, reference imbalance, and stale node consequence, but not a demonstrated reclaim or privilege escalation primitive. ## 4. Severity interpretation This is not an ordinary low-risk DoS. Conservatively, it is an Actionable Moderate issue because it combines a network packet path with a real lifetime/reference bug and plausible kernel crash. The realistic demonstrated impact is DoS under a special timeout configuration. The theoretical worst case is broader UAF-style memory corruption from a stale rhashtable node in a common packet-processing path. The patch does not demonstrate attacker-controlled reclaim, arbitrary write, type confusion, or a practical LPE chain, so the conservative score should not be treated as confirmed Important. However, the paranoid score is high enough for Important-candidate manual review. ## 5. One-sentence report phrase A race in inet fragment queue creation can arm the timer before rhashtable publication, allowing immediate timer expiry with zero or negative fragment timeout to leave a stale hash node and create a network-triggerable DoS or UAF candidate. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a race and real lifetime corruption issue in a common network fragment reassembly path, with a stale rhashtable node that is plausibly UAF-relevant. The main practical limiter is the non-default timeout condition, but the memory lifetime class and network reachability make autoclose unsafe. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: inet: frags: publish queues before arming timer Commit: 9f904dd3e455750e5d4ec9b2f134835811b85a2f Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9f904dd3e455750e5d4ec9b2f134835811b85a2f Commit description: inet_frag_create() arms the fragment queue timer before inserting the queue into the fqdir rhashtable. If the namespace fragment timeout is zero or negative, the timer can run before the queue is published. The timer callback then marks the queue complete, tries to remove a node that is not in the hash table yet, and drops the anticipated hash reference. Creation can subsequently publish the completed queue without restoring that reference, leaving a stale hash node after the caller drops the remaining reference. Publish the queue first and arm the timer while holding the queue lock. This makes timer expiry wait until the queue is visible in the hash table, so inet_frag_kill() can remove the node and balance the hash reference. Fixes: 648700f ("inet: frags: use rhashtables for reassembly units") Cc: stable@vger.kernel.org Reported-by: Vega Signed-off-by: Zhiling Zou Signed-off-by: Ren Wei Link: https://patch.msgid.link/bf66785e7c0c139d7a1900e2f01faeeab344b960.1784948849.git.zhilinz@nebusec.ai Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/ipv4/inet_fragment.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=9f904dd3e455750e5d4ec9b2f134835811b85a2f ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74662 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74662 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: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: 5 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).