From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74492][MODERATE 7.0] netfilter: ipset: do not update comments from kernel-side hash adds Date: Sat, 15 Aug 2026 09:23:32 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74492 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: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 661ff9c0cfbe07f8eed920dde9f7781491738207 List-Id: CVE: CVE-2026-74492 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: netfilter: ipset: do not update comments from kernel-side hash adds Commit: 661ff9c0cfbe07f8eed920dde9f7781491738207 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=661ff9c0cfbe07f8eed920dde9f7781491738207 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74492 Analysis date: Sat, 15 Aug 2026 09:23:32 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A packet-triggerable ipset comment lifetime race during hash resize can leave a replacement-table entry with a stale comment pointer, causing a UAF dereference during backlog replay and a kernel crash, with limited memory-corruption concern requiring manual review. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74492 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74492 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-2026-74492 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;CWE-825;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'An ipset comment UAF can occur during hash resize because mtype_resize copies ip_set_comment_rcu pointers rather than comment objects. During the race window, packet-side xt_SET add-set exist updates may hit the old published table and free comment storage that is also referenced by the replacement table. A later backlog replay on the new table can call ip_set_init_comment and strlen on the stale pointer, causing a kernel crash and possible limited memory corruption impact. For the CVSS the PR:N because a remote packet sender can trigger packet-side set updates once a vulnerable ipset with comments and an xt_SET add-set exist rule is already configured. The issue is network reachable through packet processing, but exploitation requires a specific firewall configuration and a resize race, so AC:H is appropriate. Impact is at least denial of service via kernel crash. In the paranoid score, limited confidentiality or integrity impact is kept for manual-review sensitivity because the primitive is a UAF stale pointer dereference, but no strong arbitrary write primitive is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) SKIP CVE-2026-74492 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE REMOTE SIMPLEFIX NETFILTER KPANIC PACKET KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum** ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2 Packet-side `xt_SET --add-set --exist` updates can be triggered by network traffic once the vulnerable ipset and rule are configured. * Memory corruption, weak/indirect corruption candidate: +1 The bug creates a stale `ip_set_comment_rcu` pointer and later dereferences it through `strlen()`. This is a UAF dereference, but no arbitrary write, callback control, type confusion, or attacker-controlled reclaim is shown. * Real lifetime corruption: +1 The old and replacement hash-table entries temporarily share the same comment pointer. Packet-side update can free the shared object while the replacement entry still references it. * Reliable kernel crash / strong DoS: +1 The stale pointer is later dereferenced during backlog replay, which can cause a kernel crash. * Common networking core path or packet-processing path: +1 The affected path is netfilter/ipset packet-side rule processing. * Hard or unreliable race / special timing required: -1 Exploitation requires hitting the resize window before table swap and backlog replay. Conservative total: 5 Paranoid additional signals: * Confidentiality impact plausible: +1 A stale pointer dereference in `strlen()` is primarily an invalid read, but limited disclosure or secondary effects cannot be fully excluded without deeper allocator and reclaim analysis. * Integrity impact plausible: +1 Integrity impact is not demonstrated, but limited memory corruption concern is defensible for manual triage because this is a real UAF lifetime bug in packet processing. Paranoid total: 7 Not awarded: * Strong LPE plausibility: +0 No controlled reclaim, overwrite, callback dispatch, type confusion, refcount takeover, or arbitrary write is shown. * Dirty-Pipe-like or COW violation: +0 No shared page, page cache, file-backed ownership, or COW boundary violation is involved. * Requires admin/root/CAP_NET_ADMIN: 0 Admin privileges are needed to create the vulnerable ipset/rule configuration, but the trigger can be a remote packet sender once that configuration exists. ## 3. Reachability analysis The bug is reachable through netfilter ipset packet-side updates when a system uses an ipset with comments and an `xt_SET --add-set --exist` rule. A remote sender can potentially trigger the packet-side add path if traffic reaches a rule that performs set updates. The vulnerable condition also requires a concurrent hash resize and the narrow window where the old table is still published while the replacement table already shares copied comment pointers. Namespaces and containers matter mainly for configuration. Creating or modifying ipsets normally requires `CAP_NET_ADMIN`, but a remote attacker does not need that capability if the firewall is already configured in the vulnerable way. This is not a default exposure for every Linux host, but it is still a realistic packet-processing path in deployments using ipset-based dynamic firewall rules. ## 4. Severity interpretation This is more than an ordinary Moderate issue because it is a real lifetime bug in a network packet-processing path and can be remotely triggered under a plausible firewall configuration. The conservative interpretation is Actionable Moderate because the demonstrated primitive is UAF dereference leading to DoS with a hard race. The paranoid interpretation reaches Strong Important candidate because the bug class is UAF in netfilter packet processing and the trigger may be remote. However, the evidence supports only stale pointer dereference and crash with possible limited C/I concern, not a strong privilege-escalation primitive. ## 5. One-sentence report phrase A packet-triggerable ipset comment lifetime race during hash resize can leave a replacement-table entry with a stale comment pointer, causing a UAF dereference during backlog replay and a kernel crash, with limited memory-corruption concern requiring manual review. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a network-reachable netfilter packet-processing UAF candidate with a real stale pointer lifetime bug. Even though the demonstrated impact is mainly DoS and the race is hard, the combination of packet-side trigger, UAF dereference, and netfilter exposure should not be auto-closed. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfilter: ipset: do not update comments from kernel-side hash adds Commit: 661ff9c0cfbe07f8eed920dde9f7781491738207 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=661ff9c0cfbe07f8eed920dde9f7781491738207 Commit description: mtype_resize() copies comment pointers with memcpy(), not the comment objects themselves. During the window after an entry has been copied but before the table swap and backlog replay, the old table is still published for packet-side updates while the replacement-table entry already holds the same ip_set_comment_rcu pointer. If xt_SET --add-set ... --exist hits that old entry in this window, mtype_add() calls ip_set_init_comment() even though packet-side adds carry no comment payload. That call frees the shared comment through the old entry, so the replacement-table entry now holds a stale pointer. When the queued add is replayed on the new table, mtype_add() calls ip_set_init_comment() again and strlen() dereferences the stale pointer. Fix this in mtype_add() by skipping ip_set_init_comment() when ext->target marks a packet-side add. Userspace adds still update comments, while packet-side adds can no longer free comment storage shared with a resize copy. Fixes: f66ee04 ("netfilter: ipset: Fix "INFO: rcu detected stall in hash_xxx" reports") Cc: stable@vger.kernel.org Signed-off-by: David Lee Assisted-by: Codex:gpt-5.5 Acked-by: Jozsef Kadlecsik Signed-off-by: Pablo Neira Ayuso Signed-off-by: Greg Kroah-Hartman Changed files: net/netfilter/ipset/ip_set_hash_gen.h 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=661ff9c0cfbe07f8eed920dde9f7781491738207 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74492 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74492 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:L/I:L/A:H The Best / paranoid CVSS score: 7 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: 7 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).