net: extend IPv6 exthdr detection of tunneled packets

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-98852
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-18 16:17:39 UTC
Updated2026-10-21 13:21:49 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net: extend IPv6 exthdr detection of tunneled packets Commit c4336a07eb6b ("net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback") split skb_gso_has_extension_hdr() into mutually exclusive branches on skb->encapsulation. This did not yet address all paths: 1. With skb->encapsulation set, the outer header is not checked. IPv6 tunnels such as ip6_gre and ip6_tunnel add an outer Destination Options header by default (encap_limit). Their GSO packets skip software GSO, then skb_csum_hwoffload_help() sees the outer extension header and calls skb_checksum_help() on the GSO skb, which warns and drops it. 2. Tunnels over IPv6 without an outer transport header, such as ip6_tunnel, leave skb->transport_header at the inner transport header. skb_network_header_len() then spans the outer IPv6, tunnel and inner IP headers, a false positive. 3. UDP tunnels without an inner network header, such as SCTP-in-UDP or PSP, have no inner IPv6 header to check. Decide on the outer header alone. 4. Directly dereferencing inner_ip_hdr(skb)->version without skb_header_pointer() is unsafe. Instead, check ipv6_ext_hdr(nexthdr) on the outer IPv6 header and, if set, on the inner IPv6 header. Read the headers with skb_header_pointer(). Keep the skb_network_header_len() check when !skb->encapsulation to also catch encapsulated packets without skb->encapsulation (e.g., virtio). Use the same helper in skb_csum_hwoffload_help(). Its open coded test has the false positive of (2) and ignores the inner header. Background: checksum offload of tunneled packets invariants: Non-GSO skb: - If the inner packet is CHECKSUM_PARTIAL, Local Checksum Offload computes the outer checksum in software and the device offloads only the inner L4 checksum. - If the inner packet is CHECKSUM_NONE (e.g., SCTP-in-UDP, ESP-in-UDP, Remote Checksum Offload), the device offloads the outer UDP or GRE checksum instead. GSO skb: - A device with NETIF_F_GSO_UDP_TUNNEL_CSUM or NETIF_F_GSO_GRE_CSUM computes both inner and outer checksums per segment. The outer checksum is seeded with only the pseudo-header checksum. A NETIF_F_IPV6_CSUM device must parse through the outer headers to reach the inner ones.

Risk And Classification

EPSS: 0.001570000 probability, percentile 0.044430000 (date 2026-10-21)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected ed71cf465c75f5688b07a35d373cd1d6b589c8ea fdbd83c2d929ec968b37d2f75149a79440e328ff git Not specified
CNA Linux Linux affected 33670f780e0120c3dacda188c512bbffe0b6044c 44ba9dc568c878b699d05e7cf699572dc9df4b59 git Not specified
CNA Linux Linux affected a98b78116a27e2a57b696b569b2cb431c95cf9b6 aa480f05aed7a9eee87d4a6fc90647fe9679c670 git Not specified
CNA Linux Linux affected c4336a07eb6b2526dc2b62928b5104b41a7f81f5 cabacdf98e09eb74599c4d97d7bd7fd659598fb7 git Not specified
CNA Linux Linux affected c4336a07eb6b2526dc2b62928b5104b41a7f81f5 5f0764cb1c81a9712bce605d38efe6d844a70b29 git Not specified
CNA Linux Linux affected 2094a7cf91b71367b649f991aacc7b579f793d0b git Not specified
CNA Linux Linux affected 732fdeb2987c94b439d51f5cb9addddc2fc48c42 git Not specified
CNA Linux Linux affected 6.6.134 6.6.160 semver Not specified
CNA Linux Linux affected 6.12.81 6.12.113 semver Not specified
CNA Linux Linux affected 6.18.22 6.18.56 semver Not specified
CNA Linux Linux affected 6.1.168 6.2 semver Not specified
CNA Linux Linux affected 6.19.12 6.20 semver Not specified
CNA Linux Linux affected 7.0 Not specified
CNA Linux Linux unaffected 7.0 semver Not specified
CNA Linux Linux unaffected 6.6.160 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.113 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.56 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.10 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/5f0764cb1c81a9712bce605d38efe6d844a70b29 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/fdbd83c2d929ec968b37d2f75149a79440e328ff 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/44ba9dc568c878b699d05e7cf699572dc9df4b59 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/aa480f05aed7a9eee87d4a6fc90647fe9679c670 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/cabacdf98e09eb74599c4d97d7bd7fd659598fb7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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