Description
In 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.
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.
Published:
2026-10-18
Score:
n/a
EPSS:
n/a
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
Analysis and contextual insights are available on OpenCVE Cloud.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
|||||||||||||||||||||||||||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
No vendor fix or workaround currently provided.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
Sign in to view the affected projects.
Advisories
No advisories yet.
References
History
Sun, 18 Oct 2026 16:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In 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. | |
| Title | net: extend IPv6 exthdr detection of tunneled packets | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-18T15:50:55.946Z
Reserved: 2026-09-25T10:25:14.376Z
Link: CVE-2026-98852
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-18T16:17:39.593
Modified: 2026-10-18T16:17:39.593
Link: CVE-2026-98852
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.