--- id: CVE-2026-43037 title: |- In the Linux kernel, the following vulnerability has been resolved: ip6_tunnel: clear skb2->cb[] in ip4ip6_err() Oskar Kjos reported the following problem. ip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written by the I… summary: |- In the Linux kernel, the following vulnerability has been resolved: ip6_tunnel: clear skb2->cb[] in ip4ip6_err() Oskar Kjos reported the following problem. ip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written by the I… severity: critical cvss: 9.8 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H' cwe: - CWE-787 - CWE-843 published: '2026-05-01' updated: '2026-06-27' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-43037' references: - url: 'https://git.kernel.org/stable/c/1063515ce15ff31065c4e7f8265f4c2fd3c54876' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/2edfa31769a4add828a7e604b21cb82aaaa05925' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/4a622658f384b03560834cbe8ffcfe69a278f7c8' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/a0c4ce9900a108eaf55d0f3b399cb55999647d39' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/d6621f60192fe10c047a4487be42a6f4c150707f' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/ea9f65b27c8404e164848ebff1443310fd187629' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://access.redhat.com/errata/RHSA-2026:22900' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:22940' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:22964' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:23224' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:23237' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:24343' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:25120' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:25121' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:25181' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:25186' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:25191' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:25193' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:25200' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:25217' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:25533' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:25534' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:26528' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:26535' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:26542' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:27719' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:27729' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:28738' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:28740' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:28741' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:28742' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:28748' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:28749' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/errata/RHSA-2026:28750' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://access.redhat.com/security/cve/CVE-2026-43037' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2464351' label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: >- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-43037.json label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c - url: 'https://www.cve.org/CVERecord?id=CVE-2026-43037' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-43037' - url: >- https://lore.kernel.org/linux-cve-announce/2026050102-CVE-2026-43037-0346@gregkh/T - url: 'https://access.redhat.com/errata/RHSA-2026:33486' - url: 'https://access.redhat.com/errata/RHSA-2026:41236' - url: 'https://access.redhat.com/errata/RHSA-2026:28887' - url: 'https://access.redhat.com/errata/RHSA-2026:28962' - url: 'https://access.redhat.com/errata/RHSA-2026:25044' - url: 'https://access.redhat.com/errata/RHSA-2026:34098' - url: 'https://access.redhat.com/errata/RHSA-2026:44232' tags: - nvd - csaf - vex - red-hat - cve.org epss: 0.00688 epssPercentile: 0.52508 ingestedAt: '2026-06-29T13:24:34.833Z' vendor: Red Hat product: Red Hat Enterprise Linux BaseOS E4S (v.9.4) affected: - enterprise_linux 9 - nvidia_for_rhel 10 - enterprise_linux_server_extension_v_6_els_extension - enterprise_linux_server_optional_extension_v_6_els_extension - enterprise_linux_server_v_7_els - enterprise_linux_for_real_time_v_7_els - enterprise_linux_server_optional_v_7_els - openshift_container_platform 4.12 - openshift_container_platform 4.13 - openshift_container_platform 4.14 - openshift_container_platform 4.15 - openshift_container_platform 4.16 - openshift_container_platform 4.17 - openshift_container_platform 4.18 - openshift_container_platform 4.19 - openshift_container_platform 4.20 - openshift_container_platform 4.21 - openshift_container_platform 4.22 - enterprise_linux_appstream_eus_v_10_0 - enterprise_linux_appstream_v_10 - enterprise_linux_appstream_e4s_v_9_2 - enterprise_linux_appstream_e4s_v_9_4 - enterprise_linux_appstream_eus_v_9_6 - enterprise_linux_appstream_v_9 - enterprise_linux_baseos_eus_v_10_0 - enterprise_linux_baseos_v_10 - enterprise_linux_baseos_v_8 - enterprise_linux_baseos_aus_v_8_4 - enterprise_linux_baseos_eus_extension_v_8_4 - enterprise_linux_baseos_aus_v_8_6 - enterprise_linux_baseos_eus_extension_v_8_6 - enterprise_linux_baseos_e4s_v_8_8 - enterprise_linux_baseos_tus_v_8_8 - enterprise_linux_baseos_e4s_v_9_2 - enterprise_linux_baseos_e4s_v_9_4 - enterprise_linux_baseos_eus_v_9_6 - enterprise_linux_baseos_v_9 - enterprise_linux_codeready_linux_builder_eus_v_10_0 - enterprise_linux_codeready_linux_builder_v_10 - enterprise_linux_crb_v_8 patched: - nvidia_for_rhel 10 - enterprise_linux_server_extension_v_6_els_extension - enterprise_linux_server_optional_extension_v_6_els_extension - enterprise_linux_server_v_7_els - enterprise_linux_for_real_time_v_7_els - enterprise_linux_server_optional_v_7_els - openshift_container_platform 4.12 - openshift_container_platform 4.13 - openshift_container_platform 4.14 - openshift_container_platform 4.15 - openshift_container_platform 4.16 - openshift_container_platform 4.17 - openshift_container_platform 4.18 - openshift_container_platform 4.19 - openshift_container_platform 4.20 - openshift_container_platform 4.21 - openshift_container_platform 4.22 - enterprise_linux_appstream_eus_v_10_0 - enterprise_linux_appstream_v_10 - enterprise_linux_appstream_e4s_v_9_2 - enterprise_linux_appstream_e4s_v_9_4 - enterprise_linux_appstream_eus_v_9_6 - enterprise_linux_appstream_v_9 - enterprise_linux_baseos_eus_v_10_0 - enterprise_linux_baseos_v_10 - enterprise_linux_baseos_v_8 - enterprise_linux_baseos_aus_v_8_4 - enterprise_linux_baseos_eus_extension_v_8_4 - enterprise_linux_baseos_aus_v_8_6 - enterprise_linux_baseos_eus_extension_v_8_6 - enterprise_linux_baseos_e4s_v_8_8 - enterprise_linux_baseos_tus_v_8_8 - enterprise_linux_baseos_e4s_v_9_2 - enterprise_linux_baseos_e4s_v_9_4 - enterprise_linux_baseos_eus_v_9_6 - enterprise_linux_baseos_v_9 - enterprise_linux_codeready_linux_builder_eus_v_10_0 - enterprise_linux_codeready_linux_builder_v_10 - enterprise_linux_crb_v_8 - codeready_linux_builder_eus_v_9_6 scores: nvd: 9.8 vendor: 8.8 cna: 9.8 ssvc: exploitation: none automatable: 'yes' technicalImpact: total timestamp: '2026-10-16T15:13:48.832750Z' --- ## Overview In the Linux kernel, the following vulnerability has been resolved: ip6_tunnel: clear skb2->cb[] in ip4ip6_err() Oskar Kjos reported the following problem. ip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written by the IPv6 receive path as struct inet6_skb_parm. icmp_send() passes IPCB(skb2) to __ip_options_echo(), which interprets that cb[] region as struct inet_skb_parm (IPv4). The layouts differ: inet6_skb_parm.nhoff at offset 14 overlaps inet_skb_parm.opt.rr, producing a non-zero rr value. __ip_options_echo() then reads optlen from attacker-controlled packet data at sptr[rr+1] and copies that many bytes into dopt->__data, a fixed 40-byte stack buffer (IP_OPTIONS_DATA_FIXED_SIZE). To fix this we clear skb2->cb[], as suggested by Oskar Kjos. Also add minimal IPv4 header validation (version == 4, ihl >= 5). ## Remediation Refer to the linked advisories for vendor-supplied fixes and affected version ranges. ## Vendor advisories - **RHSA-2026:25534** · Red Hat · fixed in: NVIDIA for RHEL 10 · released 2026-06-12 · [advisory](https://access.redhat.com/errata/RHSA-2026:25534) - **RHSA-2026:33486** · Red Hat · fixed in: NVIDIA for RHEL 10 · released 2026-06-30 · [advisory](https://access.redhat.com/errata/RHSA-2026:33486) - **RHSA-2026:27719** · Red Hat · fixed in: Red Hat Enterprise Linux Server -EXTENSION(v. 6 ELS-EXTENSION), Red Hat Enterprise Linux Server Optional -EXTENSION (v. 6 ELS -EXTENSION) · released 2026-06-22 · [advisory](https://access.redhat.com/errata/RHSA-2026:27719) - **RHSA-2026:27729** · Red Hat · fixed in: Red Hat Enterprise Linux Server (v. 7 ELS), Red Hat Enterprise Linux Server Optional (v. 7 ELS) · released 2026-06-22 · [advisory](https://access.redhat.com/errata/RHSA-2026:27729) - **RHSA-2026:41236** · Red Hat · fixed in: Red Hat Enterprise Linux for Real Time (v. 7 ELS) · released 2026-07-17 · [advisory](https://access.redhat.com/errata/RHSA-2026:41236) - **RHSA-2026:26528** · Red Hat · fixed in: Red Hat OpenShift Container Platform 4.12 · released 2026-06-25 · [advisory](https://access.redhat.com/errata/RHSA-2026:26528) - **RHSA-2026:26542** · Red Hat · fixed in: Red Hat OpenShift Container Platform 4.13 · released 2026-06-25 · [advisory](https://access.redhat.com/errata/RHSA-2026:26542) - **RHSA-2026:28887** · Red Hat · fixed in: Red Hat OpenShift Container Platform 4.14 · released 2026-07-01 · [advisory](https://access.redhat.com/errata/RHSA-2026:28887) - **RHSA-2026:28962** · Red Hat · fixed in: Red Hat OpenShift Container Platform 4.15 · released 2026-07-06 · [advisory](https://access.redhat.com/errata/RHSA-2026:28962) - **RHSA-2026:25044** · Red Hat · fixed in: Red Hat OpenShift Container Platform 4.16 · released 2026-06-18 · [advisory](https://access.redhat.com/errata/RHSA-2026:25044) - **RHSA-2026:34098** · Red Hat · fixed in: Red Hat OpenShift Container Platform 4.17 · released 2026-07-09 · [advisory](https://access.redhat.com/errata/RHSA-2026:34098) - **Red Hat VEX** · Critical · affected: Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 9 · updated 2026-10-09 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-43037.json)