From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53275][MODERATE 7.0] ipv6: mcast: Fix use-after-free when processing MLD queries Date: Thu, 25 Jun 2026 08:57:01 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53275 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: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 1354271c89d0e5fbf8b3d94097ff0216695209c7 List-Id: CVE: CVE-2026-53275 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: ipv6: mcast: Fix use-after-free when processing MLD queries Commit: 1354271c89d0e5fbf8b3d94097ff0216695209c7 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1354271c89d0e5fbf8b3d94097ff0216695209c7 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53275 Analysis date: Thu, 25 Jun 2026 08:57:01 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: An adjacent-network attacker may trigger a stale skb header pointer dereference in IPv6 MLD query processing after `pskb_may_pull()` reallocates the header, causing a use-after-free read and likely kernel DoS. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53275 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53275 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-2026-53275 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-825;*CWE-20;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'IPv6 MLD query processing can dereference a stale multicast group address pointer after pskb_may_pull reallocates the skb header, resulting in a use-after-free read in __mld_query_work. An adjacent network attacker can potentially trigger this with a crafted MLD query because MLD is an ICMPv6 link-local control protocol and is not normally routable across the Internet. For the CVSS the PR:N is used because no credentials or local account on the victim are required when the attacker is on the same L2 segment. AC:H is used because reliable triggering depends on skb layout and header reallocation conditions. Impact is at least denial of service via kernel crash. The paranoid score keeps limited confidentiality and integrity impact because this is a real UAF read in networking code, but there is no clear arbitrary write primitive in the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 6) YES REMOTE READ OOB DANGER UAF NETWORK SKB IPV6 KPANIC PACKET NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 6 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2 MLD queries are received from the network. This is best treated as adjacent-network reachable rather than Internet-routable remote exposure. * Memory corruption, weak/indirect corruption candidate: +1 The bug is a confirmed stale pointer / UAF read, but the patch shows a read of an old skb header pointer, not an attacker-controlled write, callback overwrite, or type confusion. * Real lifetime corruption: +1 The pointer survives skb header reallocation after `pskb_may_pull()` / `pskb_expand_head()`. * Reliable kernel crash / strong DoS: +1 KASAN reports slab-use-after-free in `__mld_query_work()`. Availability impact is realistic. * Common networking packet-processing path: +1 IPv6 multicast / MLD processing is a networking receive path, not a purely local control-plane interface. * Hard or unreliable trigger conditions: -1 Reliable triggering depends on skb layout and whether the header is reallocated after pull operations. Conservative total: 5 Paranoid adjustment: * Broad/default networking exposure or UAF triage sensitivity: +1 IPv6 and multicast support are common enough that a network-adjacent UAF in packet processing should not be auto-closed without review. Paranoid total: 6 ## 3. Reachability analysis An attacker needs the ability to send crafted IPv6 MLD traffic to the target on the same L2 segment or otherwise in a position where MLD packets are accepted. This is not normally Internet-routable, so AV:A is more appropriate than full AV:N in CVSS terms. No local account or credentials on the victim are required. Namespaces and containers do not materially reduce the main network-adjacent concern, because the trigger is packet reception by the host networking stack. Practical exploitation depends on network topology, IPv6 multicast handling, and skb reallocation conditions. ## 4. Severity interpretation This behaves stronger than an ordinary Moderate because it is a confirmed UAF in a network packet-processing path. However, the demonstrated primitive is a stale read from freed skb header memory, not a write-after-free, controlled object replacement, callback dispatch, or known privilege-escalation primitive. Realistic impact is primarily kernel crash / DoS. Theoretical confidentiality or integrity concerns are limited and justify manual review, but current evidence does not support treating it as a Strong Important candidate. ## 5. One-sentence report phrase An adjacent-network attacker may trigger a stale skb header pointer dereference in IPv6 MLD query processing after `pskb_may_pull()` reallocates the header, causing a use-after-free read and likely kernel DoS. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: confirmed UAF plus network-adjacent packet reachability. The available evidence supports Actionable Moderate handling, while manual review should confirm whether any reclaim, disclosure, or stronger corruption path exists beyond DoS. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ipv6: mcast: Fix use-after-free when processing MLD queries Commit: 1354271c89d0e5fbf8b3d94097ff0216695209c7 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1354271c89d0e5fbf8b3d94097ff0216695209c7 Commit description: When processing an MLD query, a pointer to the multicast group address is retrieved when initially parsing the packet. This pointer is later dereferenced without being reloaded despite the fact that the skb header might have been reallocated following the pskb_may_pull() calls, leading to a use-after-free [1]. Fix by copying the multicast group address when the packet is initially parsed. [1] BUG: KASAN: slab-use-after-free in __mld_query_work (net/ipv6/mcast.c:1512) Read of size 8 at addr ffff8881154b8e90 by task kworker/4:1/118 Workqueue: mld mld_query_work Call Trace: dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120) print_address_description.constprop.0 (mm/kasan/report.c:378) print_report (mm/kasan/report.c:482) kasan_report (mm/kasan/report.c:595) __mld_query_work (net/ipv6/mcast.c:1512) mld_query_work (net/ipv6/mcast.c:1563) process_one_work (kernel/workqueue.c:3314) worker_thread (kernel/workqueue.c:3397 kernel/workqueue.c:3478) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:158) ret_from_fork_asm (arch/x86/entry/entry_64.S:245) [...] Freed by task 118: kasan_save_stack (mm/kasan/common.c:57) kasan_save_track (mm/kasan/common.c:78) kasan_save_free_info (mm/kasan/generic.c:584) __kasan_slab_free (mm/kasan/common.c:253 mm/kasan/common.c:285) kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6251 mm/slub.c:6566) pskb_expand_head (net/core/skbuff.c:2335) __pskb_pull_tail (net/core/skbuff.c:2878 (discriminator 4)) __mld_query_work (net/ipv6/mcast.c:1495 (discriminator 1)) mld_query_work (net/ipv6/mcast.c:1563) process_one_work (kernel/workqueue.c:3314) worker_thread (kernel/workqueue.c:3397 kernel/workqueue.c:3478) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:158) ret_from_fork_asm (arch/x86/entry/entry_64.S:245) Fixes: 97300b5 ("[MCAST] IPv6: Check packet size when process Multicast") Reported-by: Leo Lin Reviewed-by: David Ahern Signed-off-by: Ido Schimmel Reviewed-by: Eric Dumazet Reviewed-by: Jiayuan Chen Link: https://patch.msgid.link/20260603101811.612594-1-idosch@nvidia.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/ipv6/mcast.c lib/dump_stack.c mm/kasan/report.c kernel/workqueue.c kernel/kthread.c arch/x86/kernel/process.c arch/x86/entry/entry_64.S mm/kasan/common.c mm/kasan/generic.c include/linux/kasan.h mm/slub.c net/core/skbuff.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=1354271c89d0e5fbf8b3d94097ff0216695209c7 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53275 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53275 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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 6.4 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: 6 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).