From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74582][IMPORTANT] packet: use consistent hard_header_len in non-ring send paths Date: Fri, 21 Aug 2026 12:57:57 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74582 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: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 91f041451f967cd87ed722a8f43c0b767a64f1a0 List-Id: CVE: CVE-2026-74582 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: packet: use consistent hard_header_len in non-ring send paths Commit: 91f041451f967cd87ed722a8f43c0b767a64f1a0 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91f041451f967cd87ed722a8f43c0b767a64f1a0 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74582 Analysis date: Fri, 21 Aug 2026 12:57:57 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: AF_PACKET non-ring send paths can use inconsistent hard_header_len values during concurrent device reconfiguration, causing skb head underflow and a userspace-driven out-of-bounds kernel write with local DoS and possible privilege escalation impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74582 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74582 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-2026-74582 IMPORTANT CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-362;CWE-367;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'AF_PACKET non-ring send paths can read dev hard_header_len inconsistently while a network device is being reconfigured. In the SOCK_RAW path, packet_snd can keep a larger reserve value but allocate skb headroom using a smaller later value, so moving skb data back may place it before skb head and the following userspace copy can become an out-of-bounds kernel write. For the CVSS the PR:L is used for the paranoid score because reliable triggering may require local capabilities such as CAP_NET_RAW and CAP_NET_ADMIN in a network namespace, but this is not always equivalent to full host administrator privileges. The issue is not directly network reachable because it is triggered through local AF_PACKET send operations and concurrent local device reconfiguration. Impact is at least local denial of service via kernel memory corruption and in the worst case may allow confidentiality or integrity impact including privilege escalation. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES WRITE OOB SKB HARDWARE IPV6 KPANIC PACKET KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 NO NO 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 Triggered signals: * Memory corruption, Strong corruption primitive: +2 The commit explicitly describes an out-of-bounds write caused by moving skb->data before skb->head, followed by a userspace copy. * Memory layout invariant restoration: +1 The fix restores consistency between hard_header_len, reserve, headroom allocation, and skb construction. * Reliable kernel crash / strong DoS: +1 An skb head underflow followed by copy from userspace is a credible kernel crash condition. * Weak LPE concern: +1 conservative, Strong LPE plausibility: +2 paranoid Conservative view: no demonstrated reclaim or target selection is shown. Paranoid view: attacker-influenced data is copied out of bounds in kernel memory, so privilege escalation is technically plausible and requires manual review. * Common networking / packet socket path: +1 AF_PACKET is a common kernel networking interface, although triggering this specific bug depends on local send paths and concurrent device reconfiguration. Subtractors: * Hard or unreliable race / special timing required: -1 The bug requires a race between AF_PACKET send path execution and net_device hard_header_len changes. * Requires capabilities in typical deployments: -1 conservative Reliable triggering likely needs CAP_NET_RAW for AF_PACKET SOCK_RAW and CAP_NET_ADMIN or equivalent control over device reconfiguration. This is not full host root in all namespace or container models, so -1 is used rather than a full -2. ## 3. Reachability analysis The bug is local, not directly network reachable. Triggering requires local AF_PACKET send operations and concurrent reconfiguration of a network device whose hard_header_len can change, such as bonding device type changes. In typical deployments, AF_PACKET SOCK_RAW requires CAP_NET_RAW, and the relevant device reconfiguration path usually requires CAP_NET_ADMIN. In containerized or user namespace enabled environments, those capabilities may be delegated in a way that is weaker than full host root, so PR:L style treatment is defensible for triage. The path is not a remote packet parsing path. Realistic exploitation requires local code execution plus timing control over sendmsg and device reconfiguration. ## 4. Severity interpretation This should not be treated as an ordinary Moderate auto-close issue. The bug is a race, but the resulting primitive is stronger than a NULL dereference or bookkeeping mismatch because it can cause an out-of-bounds kernel write with userspace-provided data. Conservative interpretation is Actionable Moderate because exploitation requires local capabilities and a race. Paranoid interpretation is a Strong Important candidate because the patch context explicitly supports kernel memory corruption in a common networking subsystem and the LPE potential cannot be ruled out without manual analysis. ## 5. One-sentence report phrase AF_PACKET non-ring send paths can use inconsistent hard_header_len values during concurrent device reconfiguration, causing skb head underflow and a userspace-driven out-of-bounds kernel write with local DoS and possible privilege escalation impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch fixes a race leading to an explicit out-of-bounds kernel write from userspace data in AF_PACKET skb construction, so privilege escalation feasibility and namespace/capability reachability should be reviewed manually. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: packet: use consistent hard_header_len in non-ring send paths Commit: 91f041451f967cd87ed722a8f43c0b767a64f1a0 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91f041451f967cd87ed722a8f43c0b767a64f1a0 Commit description: packet_snd() reads dev->hard_header_len multiple times while allocating and constructing an skb. Device reconfiguration can change this value concurrently, for example through bonding device type changes. For SOCK_RAW, packet_snd() can save a larger value in reserve and later allocate headroom using a smaller value. Moving skb->data back by reserve then places it before skb->head, and the following copy from userspace can attempt an out-of-bounds write. packet_sendmsg_spkt() has the same issue because it calculates its reservation and header offset from separate reads before dropping the RCU read lock to allocate the skb. Add LL_RESERVED_SPACE_EX() for callers that already saved a header length. Read hard_header_len once in packet_snd() and use it for allocation and construction. In packet_sendmsg_spkt(), preserve the allocation-time value through the device lookup retry. The separate SOCK_DGRAM consistency problem between hard_header_len and header_ops->create is not addressed here. Fixes: b84bbaf ("packet: in packet_snd start writing at link layer allocation") Cc: stable@vger.kernel.org Signed-off-by: Qihang Tang Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260805125729.19220-3-q.h.hack.winter@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: include/linux/netdevice.h net/packet/af_packet.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=91f041451f967cd87ed722a8f43c0b767a64f1a0 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74582 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74582 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:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/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: 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).