From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80978][MODERATE 7.0] net: cap advertised IP tunnel headroom Date: Fri, 11 Sep 2026 16:08:12 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80978 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: bc4e05ae66c9797a0972ac44326e69c5305e0020 List-Id: CVE: CVE-2026-80978 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: net: cap advertised IP tunnel headroom Commit: bc4e05ae66c9797a0972ac44326e69c5305e0020 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bc4e05ae66c9797a0972ac44326e69c5305e0020 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80978 Analysis date: Fri, 11 Sep 2026 16:08:12 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80978 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80978 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-2026-80978 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80978 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-190;*CWE-787;CWE-119;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'IP tunnel devices could advertise a needed_headroom value derived from lower devices without applying the runtime cap used on the transmit path. A stack of locally created tunnel devices can make this value exceed what 16-bit skb header offsets can represent, and later skb head expansion can wrap those offsets during skb_headers_offset_update(). For the CVSS the PR:L because reliable triggering requires a local process able to create or configure tunnel devices, often through CAP_NET_ADMIN or delegated network namespace rights. The issue is not directly network reachable by packet traffic alone. Packets may exercise the corrupted transmit path only after the local tunnel stack has been configured. Impact is at least denial of service via kernel crash, and in the paranoid case may include confidentiality or integrity impact because skb metadata offset wraparound is a memory corruption candidate.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) YES REMOTE SKB HARDWARE IPV6 KPANIC PACKET KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 PrimitiveClass=CLASS_B RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 4 * Conservative score: 5 * Applied conservative floor/cap: 4 -> 5 because a concrete active skb metadata corruption primitive is established and should not be auto closed as ordinary DoS. * Raw paranoid score: 6 * Paranoid score: 6 * Applied paranoid floor/cap: none * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Positive signals: * +2: Active kernel metadata corruption candidate. User-created IP tunnel stacking can make advertised needed_headroom exceed what 16-bit skb header offsets can represent, and skb head expansion can wrap those offsets in skb_headers_offset_update(). * +1: Memory layout invariant restoration. The patch restores consistency between published headroom, runtime headroom capping, and the representable skb header-offset range. * +1: Reliable DoS or strong availability concern. Wrapped skb header offsets in the transmit path can plausibly lead to invalid skb metadata use and kernel crash or packet-path malfunction. * +1: Common networking skb path. The affected state is consumed by IP output and skb head expansion, not just a passive diagnostic field. Negative signals: * -1 conservative: reliable triggering requires local ability to create or configure stacked tunnel devices, normally requiring CAP_NET_ADMIN or equivalent delegated network-management privilege. Host-admin-equivalent privilege is not positively established, so -2 is not used. Paranoid-only signal: * +1 paranoid: weak exploitation concern. The corrupted value is an active skb offset used by later packet processing, so impact beyond immediate crash is unresolved enough to require manual review. This does not prove arbitrary write, controlled reclaim, or LPE. Non-awarded signals: * RealUAF not awarded. This is not a lifetime or stale-object bug. * CLASS_A not awarded. The patch establishes skb metadata offset wraparound, but not an arbitrary write, controlled object replacement, controlled reclaim, callback control, or demonstrated privilege escalation. * Remote reachability not awarded. Packet traffic alone does not create the vulnerable tunnel stack. * Local unprivileged trigger not awarded. Full below-host-admin reachability through user and network namespaces is plausible in some deployments but not established by the supplied evidence. * Confidentiality and integrity bonuses not awarded directly. They remain unresolved consequences of metadata corruption, not demonstrated leak or write primitives. * Extra availability not awarded. The same crash or packet-path failure is not double-counted. 3. Reachability analysis The realistic trigger requires creating a stack of IP tunnel devices whose derived needed_headroom grows beyond the 16-bit skb header offset range, then causing traffic through the resulting output path so skb head expansion applies the excessive reservation. This is local control-plane reachability, not direct remote packet reachability. The attacker likely needs CAP_NET_ADMIN or equivalent authority to create and configure IP tunnel devices. In Linux, some tunnel and rtnetlink operations can be namespace scoped, but the supplied evidence does not prove that the complete trigger chain is available to an ordinary unprivileged user in an attacker-created user or network namespace. Therefore HostAdminRequired is UNKNOWN and NamespaceScopedPrivilege is UNKNOWN. No special physical hardware is required. No firmware mediation is involved. This is not a timing race. The configuration and transmit trigger appear repeatable once the tunnel stack can be created. 4. Primitive and severity interpretation The exact primitive is integer overflow or wraparound of 16-bit skb header-offset metadata caused by publishing an unbounded tunnel needed_headroom value to upper layers. The affected object is active structured skb metadata, not fixed stale storage and not a cleanup-only path. This is CLASS_B because it is a concrete kernel corruption or active-state consistency primitive, but exploitation leverage beyond crash is unresolved. It is not CLASS_A because there is no demonstrated arbitrary or directed kernel write, no controlled reclaim, no callback or function-pointer control, and no demonstrated LPE. The demonstrated consequence is at least DoS or packet-path corruption through invalid skb header offsets. The speculative consequence is stronger memory-corruption impact if later skb processing consumes wrapped offsets in a security-useful way. That possibility is technically plausible enough for manual review, but not enough to claim proven privilege escalation. ImportantCandidate is YES because active skb metadata corruption in a common packet path should not be automatically downgraded without reviewing downstream offset consumers. AutoDowngradeAllowed is NO because the patch-supported primitive is not a pure warning, resource leak, or ordinary crash-only validation bug. 5. One-sentence report phrase Stacked IP tunnel devices can publish an excessive needed_headroom value that wraps 16-bit skb header offsets during skb head expansion, creating an active skb metadata corruption primitive with at least DoS impact and unresolved exploitation leverage. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the bug establishes skb header-offset wraparound in an active networking data path, which is stronger than ordinary DoS even though arbitrary write or privilege escalation is not demonstrated. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: cap advertised IP tunnel headroom Commit: bc4e05ae66c9797a0972ac44326e69c5305e0020 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bc4e05ae66c9797a0972ac44326e69c5305e0020 Commit description: IP tunnel devices derive their advertised needed_headroom from lower output devices. A stack of user-created devices can make the derived value larger than the 16-bit skb header offsets can represent. Once IP output reserves it, skb head expansion can wrap those offsets. The runtime transmit path already caps a growing needed_headroom at 512. Apply the same cap when tunnel configuration publishes needed_headroom derived from a lower output device. Capping the advertised value is safe: IP tunnel transmit still expands the skb when a packet needs more headroom. A nonsensical stacked configuration can therefore incur an extra reallocation, but it cannot publish an unbounded reservation to upper layers. Fixes: 1a37e41 ("net: Use 16bits for *_headers fields of struct skbuff") Cc: stable@vger.kernel.org Reported-by: Vega Signed-off-by: Zhiling Zou Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/ba04a1fd6bfae2377607fad5d8f80f7eb80fd4c4.1786542637.git.zhilinz@nebusec.ai Signed-off-by: Paolo Abeni Signed-off-by: Greg Kroah-Hartman Changed files: include/net/ip_tunnels.h net/ipv4/ip_tunnel.c net/ipv6/ip6_gre.c net/ipv6/ip6_tunnel.c net/ipv6/sit.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=bc4e05ae66c9797a0972ac44326e69c5305e0020 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80978 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80978 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: 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).