From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53260][MODERATE 7.0] tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req(). [ Upstream Date: Thu, 25 Jun 2026 08:51:35 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53260 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: b183215ff714efb747d9d5a429322ba6404b5401 List-Id: CVE: CVE-2026-53260 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req(). [ Upstream Commit: b183215ff714efb747d9d5a429322ba6404b5401 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b183215ff714efb747d9d5a429322ba6404b5401 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53260 Analysis date: Thu, 25 Jun 2026 08:51:35 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53260 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53260 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 7.0 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-2026-53260 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:H/I:H/A:H';CWE-362;*CWE-416;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.1';DESCR 'A race condition in the TCP request socket path can occur on PREEMPT_RT kernels because reqsk_queue_hash_req can be preempted after mod_timer and before rsk_refcnt is initialized. If the request timer fires in that window while the listener is being closed, reqsk_timer_handler and __inet_csk_reqsk_queue_drop can drop references that were not established yet, causing refcount underflow and a use-after-free condition. For the CVSS the PR:N value is used for the paranoid score because the vulnerable TCP request path may be reached by remote connection attempts to an exposed listening socket, although reliable exploitation also depends on PREEMPT_RT timing and listener close behavior. The base scenario is more local and controlled, but the network exposure of the TCP path makes this unsuitable for automatic closure. Impact is at least denial of service via kernel warning or crash and in worst case may allow confidentiality or integrity impact due to kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) YES REMOTE OOB DEADLOCK INIT UAF NETWORK KERNEL_PANIC_PLUS_UAF HARDWARE SYZBOT KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 YES NO guess ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 1. ActionableScore * Conservative score: 4 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: 2. Signal breakdown * Local unprivileged trigger: +1. A local user can plausibly create and close TCP listeners and generate request sockets to exercise this path. * Remote reachable / network-triggerable, paranoid only: +2. The affected code is in the TCP request socket path and may be influenced by remote connection attempts to an exposed listener, but reliable triggering also depends on listener close timing. * Memory corruption, weak primitive: +1. The report explicitly shows refcount underflow and use-after-free, but no attacker-controlled reclaim, overwrite, callback dispatch, or type confusion is demonstrated. * Real lifetime corruption: +1. The bug is a request_sock lifetime/refcount ordering race between timer setup and refcount initialization. * Reliable kernel crash / strong DoS: +1. syzbot reached refcount underflow with use-after-free warning in timer context, and panic_on_warn or later UAF behavior can produce host DoS. * Common networking core path: +1. The bug is in TCP request socket handling, a central networking path. * Hard or unreliable race / special timing required: -1. Triggering requires PREEMPT_RT preemption exactly between mod_timer() and refcount_set(), plus timer/listener-close interaction. * Race-UAF downgrade rule applied. No LPE bonus, no C/I impact bonus, and paranoid score capped at 5 because the patch does not show controlled reclaim, write-after-free, callback corruption, or refcount takeover. 3. Reachability analysis A local unprivileged user can likely exercise the issue with controlled listener creation, connection attempts, and close timing on PREEMPT_RT kernels. A remote attacker may influence the TCP request path by sending connection attempts to a reachable listening socket, but cannot usually control the listener close event unless the service behavior helps. Containers or namespaces may lower practical privileges if untrusted workloads can open TCP listeners and generate local traffic. The path is common TCP code, but the vulnerable interleaving appears specific to PREEMPT_RT timing. 4. Severity interpretation This is stronger than an ordinary Moderate because it is a real lifetime/refcount UAF in a common TCP path. It is not a clear Important-class issue from the patch alone because exploitation beyond crash is not demonstrated, and the race window is narrow. The conservative interpretation is local DoS with weak memory-corruption concern. The paranoid interpretation is Actionable Moderate because the TCP exposure and UAF class justify manual review. 5. One-sentence report phrase A PREEMPT_RT race in TCP request socket setup can allow the request timer to run before rsk_refcnt is initialized, causing refcount underflow and use-after-free with at least DoS impact and remote-influence concern for exposed TCP listeners. 6. Manual review recommendation MANUAL CHECK REQUIRED. The issue involves refcount underflow and UAF in TCP request socket lifetime management, with possible network influence, even though practical privilege escalation is not proven. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req(). [ Upstream Commit: b183215ff714efb747d9d5a429322ba6404b5401 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b183215ff714efb747d9d5a429322ba6404b5401 Changed files: lib/refcount.c include/linux/refcount.h include/net/request_sock.h net/ipv4/inet_connection_sock.c kernel/time/timer.c kernel/softirq.c kernel/smpboot.c kernel/kthread.c arch/x86/kernel/process.c arch/x86/entry/entry_64.S 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=b183215ff714efb747d9d5a429322ba6404b5401 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53260 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53260 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: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: 4 Paranoid ActionableScore: 5 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: YES Published priority for this report (same as in Subject): MODERATE 7.0 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).