From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80844][IMPORTANT] xfrm: ah6: validate routing header segments_left Date: Fri, 04 Sep 2026 14:06:07 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80844 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: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 2dc650956e4e163b879b3fb1027f9557abc5c985 List-Id: CVE: CVE-2026-80844 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: xfrm: ah6: validate routing header segments_left Commit: 2dc650956e4e163b879b3fb1027f9557abc5c985 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dc650956e4e163b879b3fb1027f9557abc5c985 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80844 Analysis date: Fri, 04 Sep 2026 14:06:07 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: AH6 can perform an attacker-influenced out-of-bounds memmove while rearranging IPv6 routing-header addresses for AH ICV processing, allowing a local raw IPv6 HDRINCL packet path to crash the kernel and requiring manual review for possible memory-corruption impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80844 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80844 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-2026-80844 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-80844 CHECK WITH IMPACT FROM ORIG NN IMPORTANT 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-20;*CWE-787;CWE-125;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'AH6 can perform out of bounds memory access while rearranging an IPv6 routing header before AH ICV calculation or verification. The bug occurs because ipv6_rearrange_rthdr assumes that segments_left is not larger than the number of addresses encoded by hdrlen, but raw IPv6 HDRINCL packets can violate this invariant. A crafted local raw IPv6 packet with a small hdrlen and a large segments_left value can make the address pointer move backwards and can pass a large length to memmove, leading to kernel memory access outside the expected routing header buffer. For the CVSS the PR:L is used because reliable triggering requires a local process able to create such raw IPv6 traffic and usually depends on local AH6 XFRM use, not merely remote packet delivery. The issue is not considered directly network reachable from the patch context. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to an out of bounds memory access primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) SKIP CVE-2026-80844 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE OOB SIMPLEFIX ERRORPATH NETWORK LINUS IPV6 KPANIC PACKET - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO ## 1. ActionableScore * Raw conservative score: 5 * Conservative score: 5 * Raw paranoid score: 6 * Paranoid score: 6 * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: No floor or cap changed the conservative score. No floor or cap changed the paranoid score. ## 2. Signal breakdown Conservative signals: * +2: Strong corruption primitive. The patch establishes an out-of-bounds `memmove()` caused by an invalid relationship between `segments_left` and `hdrlen` in an IPv6 routing header. * +1: Reliable kernel crash / strong DoS. A 4064-byte out-of-bounds access in kernel packet processing is a realistic kernel crash condition. * +1: Memory layout invariant restoration. The fix restores the required invariant between routing-header address count and `segments_left` before pointer arithmetic and copy length calculation. * +1: Attacker-controlled structured input. Raw IPv6 HDRINCL packets can carry attacker-selected `hdrlen` and `segments_left`, directly influencing the invalid pointer arithmetic and copy size. Paranoid additional signal: * +1: Weak LPE / integrity concern. The primitive is not a NULL dereference or passive invalid read. It is an attacker-influenced out-of-bounds memory operation via `memmove()`, so post-crash exploitation leverage cannot be excluded without manual review. Important non-awarded signals: * RealUAF not awarded. No use-after-free or stale lifetime object is established. * Concrete repeated release/refcount not awarded. No repeated put/free/refcount mutation exists. * Controlled reclaim not demonstrated. * Arbitrary write not demonstrated. * Confidentiality impact not awarded. No concrete disclosure path is shown. * Direct remote reachability not awarded. The described violating path is locally generated raw IPv6 HDRINCL traffic. * Extra availability point not awarded. The crash/DoS consequence is already counted once. * NamespaceScopedPrivilege=UNKNOWN because the input does not prove that the complete AH6/XFRM trigger chain is reachable inside attacker-created namespaces. ## 3. Reachability analysis The clearest trigger is a local process generating raw IPv6 HDRINCL packets with malformed routing-header state. Creating raw IPv6 packets normally requires `CAP_NET_RAW`, and reaching AH6 processing may also depend on AH6/XFRM configuration or an existing IPsec AH setup. Host-admin-equivalent privilege is not positively established for the complete trigger, so `HostAdminRequired=UNKNOWN`, not YES. However, below-host-admin reachability is also not fully proven because the complete AH6 path may depend on prior XFRM/AH policy or configuration. The issue is not scored as directly network-triggerable. The commit specifically identifies raw locally generated packets as the path that violates the invariant. Incoming packet paths may have different validation before AH6 reaches this function. No special physical hardware is required. No hard race is involved. The trigger is a malformed packet construction path, not a timing-dependent lifetime race. ## 4. Primitive and severity interpretation The exact primitive is an attacker-influenced out-of-bounds memory access in `ipv6_rearrange_rthdr()`. The invalid `segments_left` value causes address-pointer arithmetic to move outside the routing-header address array and causes a large `memmove()` length. This is not a fixed stale-storage UAF and not cleanup-only behavior. It is active packet-buffer processing with an invalid copy range. Primitive class is `CLASS_A` because a concrete out-of-bounds memory operation is directly established. The demonstrated consequence is kernel crash / DoS. The speculative but technically defensible consequence is kernel memory corruption with possible integrity impact or privilege-escalation relevance, depending on exact skb layout and copy direction. `ImportantCandidate=YES` because the primitive is stronger than ordinary DoS-only validation failure. `AutoDowngradeAllowed=NO` because automatically closing this as ordinary Moderate would discard an established kernel OOB `memmove()` corruption primitive. Operationally, this should be treated as Actionable Moderate at minimum and a Strong Important candidate requiring manual analysis of the exact AH6 output/input call paths, skb layout, and privilege boundary. ## 5. One-sentence report phrase AH6 can perform an attacker-influenced out-of-bounds memmove while rearranging IPv6 routing-header addresses for AH ICV processing, allowing a local raw IPv6 HDRINCL packet path to crash the kernel and requiring manual review for possible memory-corruption impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch establishes a concrete out-of-bounds `memmove()` in kernel networking code with attacker-controlled header fields, and the exploitability beyond DoS depends on memory-layout and call-path details not resolved by the patch alone. ## 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: xfrm: ah6: validate routing header segments_left Commit: 2dc650956e4e163b879b3fb1027f9557abc5c985 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dc650956e4e163b879b3fb1027f9557abc5c985 Commit description: AH6 rearranges routing-header addresses before computing or verifying the ICV. ipv6_rearrange_rthdr() assumes that segments_left is not larger than the number of addresses described by the routing header's hdrlen field. That assumption does not hold for raw IPv6 HDRINCL packets. A packet with hdrlen equal to 2 describes one address, but can carry an arbitrary segments_left value. With segments_left equal to 255, the function moves its address pointer 4,064 bytes backwards and passes a 4,064-byte length to memmove(), resulting in an out-of-bounds access. Validate the invariant locally before modifying the routing header or performing any address-pointer arithmetic, and propagate malformed-header errors to the existing AH6 input and output error paths. Fixes: 1da177e ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Assisted-by: avom-custom-harness:gpt-5.5-qwen3.6-mod-mix Signed-off-by: Asim Viladi Oglu Manizada Signed-off-by: Steffen Klassert Signed-off-by: Greg Kroah-Hartman Changed files: net/ipv6/ah6.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=2dc650956e4e163b879b3fb1027f9557abc5c985 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80844 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80844 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: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: 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).