{"id":"CVE-2026-98852","title":"net: extend IPv6 exthdr detection of tunneled packets","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: extend IPv6 exthdr detection of tunneled packets\n\nCommit c4336a07eb6b (\"net: correctly handle tunneled traffic on IPV6_CSUM\nGSO fallback\") split skb_gso_has_extens…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 33670f780e0120c3dacda188c512bbffe0b6044c < 44ba9dc568c878b699d05e7cf699572dc9df4b59","Linux >= a98b78116a27e2a57b696b569b2cb431c95cf9b6 < aa480f05aed7a9eee87d4a6fc90647fe9679c670","Linux >= c4336a07eb6b2526dc2b62928b5104b41a7f81f5 < cabacdf98e09eb74599c4d97d7bd7fd659598fb7","Linux >= c4336a07eb6b2526dc2b62928b5104b41a7f81f5 < 5f0764cb1c81a9712bce605d38efe6d844a70b29","Linux 2094a7cf91b71367b649f991aacc7b579f793d0b","Linux ed71cf465c75f5688b07a35d373cd1d6b589c8ea","Linux 732fdeb2987c94b439d51f5cb9addddc2fc48c42","Linux >= 6.12.81 < 6.12.113","Linux >= 6.18.22 < 6.18.56","Linux >= 6.1.168 < 6.2","Linux >= 6.6.134 < 6.7","Linux >= 6.19.12 < 6.20","Linux 7.0"],"published":"2026-10-18","updated":"2026-10-18","sourceUpdated":"2026-10-18T15:50:55.946Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98852","references":[{"url":"https://git.kernel.org/stable/c/44ba9dc568c878b699d05e7cf699572dc9df4b59"},{"url":"https://git.kernel.org/stable/c/aa480f05aed7a9eee87d4a6fc90647fe9679c670"},{"url":"https://git.kernel.org/stable/c/cabacdf98e09eb74599c4d97d7bd7fd659598fb7"},{"url":"https://git.kernel.org/stable/c/5f0764cb1c81a9712bce605d38efe6d844a70b29"}],"tags":["cve.org"],"ingestedAt":"2026-10-18T16:47:32.463Z","slug":"CVE-2026-98852","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnet: extend IPv6 exthdr detection of tunneled packets\n\nCommit c4336a07eb6b (\"net: correctly handle tunneled traffic on IPV6_CSUM\nGSO fallback\") split skb_gso_has_extension_hdr() into mutually exclusive\nbranches on skb->encapsulation. This did not yet address all paths:\n\n1. With skb->encapsulation set, the outer header is not checked. IPv6\n   tunnels such as ip6_gre and ip6_tunnel add an outer Destination\n   Options header by default (encap_limit). Their GSO packets skip\n   software GSO, then skb_csum_hwoffload_help() sees the outer extension\n   header and calls skb_checksum_help() on the GSO skb, which warns and\n   drops it.\n\n2. Tunnels over IPv6 without an outer transport header, such as\n   ip6_tunnel, leave skb->transport_header at the inner transport\n   header. skb_network_header_len() then spans the outer IPv6, tunnel\n   and inner IP headers, a false positive.\n\n3. UDP tunnels without an inner network header, such as SCTP-in-UDP or\n   PSP, have no inner IPv6 header to check. Decide on the outer header\n   alone.\n\n4. Directly dereferencing inner_ip_hdr(skb)->version without\n   skb_header_pointer() is unsafe.\n\nInstead, check ipv6_ext_hdr(nexthdr) on the outer IPv6 header and, if\nset, on the inner IPv6 header. Read the headers with skb_header_pointer().\nKeep the skb_network_header_len() check when !skb->encapsulation to also\ncatch encapsulated packets without skb->encapsulation (e.g., virtio).\n\nUse the same helper in skb_csum_hwoffload_help(). Its open coded test\nhas the false positive of (2) and ignores the inner header.\n\nBackground: checksum offload of tunneled packets invariants:\n\nNon-GSO skb:\n- If the inner packet is CHECKSUM_PARTIAL, Local Checksum Offload computes\n  the outer checksum in software and the device offloads only the inner L4\n  checksum.\n- If the inner packet is CHECKSUM_NONE (e.g., SCTP-in-UDP, ESP-in-UDP,\n  Remote Checksum Offload), the device offloads the outer UDP or GRE\n  checksum instead.\n\nGSO skb:\n- A device with NETIF_F_GSO_UDP_TUNNEL_CSUM or NETIF_F_GSO_GRE_CSUM\n  computes both inner and outer checksums per segment.\n  The outer checksum is seeded with only the pseudo-header checksum.\n\nA NETIF_F_IPV6_CSUM device must parse through the outer headers to\nreach the inner ones.\n\n## Affected\n\n- `Linux >= 33670f780e0120c3dacda188c512bbffe0b6044c < 44ba9dc568c878b699d05e7cf699572dc9df4b59`\n- `Linux >= a98b78116a27e2a57b696b569b2cb431c95cf9b6 < aa480f05aed7a9eee87d4a6fc90647fe9679c670`\n- `Linux >= c4336a07eb6b2526dc2b62928b5104b41a7f81f5 < cabacdf98e09eb74599c4d97d7bd7fd659598fb7`\n- `Linux >= c4336a07eb6b2526dc2b62928b5104b41a7f81f5 < 5f0764cb1c81a9712bce605d38efe6d844a70b29`\n- `Linux 2094a7cf91b71367b649f991aacc7b579f793d0b`\n- `Linux ed71cf465c75f5688b07a35d373cd1d6b589c8ea`\n- `Linux 732fdeb2987c94b439d51f5cb9addddc2fc48c42`\n- `Linux >= 6.12.81 < 6.12.113`\n- `Linux >= 6.18.22 < 6.18.56`\n- `Linux >= 6.1.168 < 6.2`\n- `Linux >= 6.6.134 < 6.7`\n- `Linux >= 6.19.12 < 6.20`\n- `Linux 7.0`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}