CVE-2026-98852
Status: ReceivedUnscored—
Severity—Unscored
Exploitation probability0.16 %higher than 4% of CVEs
Active exploitationNonot in the CISA catalog
Public exploitNot knownno public code found
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:
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).
Read full descriptionShow less
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:
A NETIF_F_IPV6_CSUM device must parse through the outer headers to reach the inner ones.
Technical details traces, logs and code from the original report
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. 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.
CVSS
NVD hasn't assigned a CVSS score to this CVE (common since the April 2026 policy change).
Exploitation probability (EPSS)
- Probability of exploitation in the next 30 days
- 0.16 %
- Percentile among all scored CVEs
- 4
- Score date
- 10/20/2026
EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).
Affected technologies (1)
⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.
References
Show 4 references
Raw JSON (NVD)
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{
"id": "CVE-2026-98852",
"cveTags": [],
"metrics": {},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
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"vendor": "Linux",
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{
"status": "affected",
"version": "33670f780e0120c3dacda188c512bbffe0b6044c",
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"versionType": "git"
},
{
"status": "affected",
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{
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"lessThan": "5f0764cb1c81a9712bce605d38efe6d844a70b29",
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{
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{
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"version": "732fdeb2987c94b439d51f5cb9addddc2fc48c42",
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{
"status": "affected",
"version": "6.12.81",
"lessThan": "6.12.113",
"versionType": "semver"
},
{
"status": "affected",
"version": "6.18.22",
"lessThan": "6.18.56",
"versionType": "semver"
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{
"status": "affected",
"version": "6.1.168",
"lessThan": "6.2",
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{
"status": "affected",
"version": "6.6.134",
"lessThan": "6.7",
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{
"status": "affected",
"version": "6.19.12",
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}
],
"programFiles": [
"net/core/dev.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "7.0"
},
{
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"version": "0",
"lessThan": "7.0",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "6.12.113",
"versionType": "semver",
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},
{
"status": "unaffected",
"version": "6.18.56",
"versionType": "semver",
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{
"status": "unaffected",
"version": "7.2.10",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
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"version": "7.3",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
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"programFiles": [
"net/core/dev.c"
],
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}
]
}
],
"published": "2026-10-18T16:17:39.593",
"references": [
{
"url": "https://git.kernel.org/stable/c/44ba9dc568c878b699d05e7cf699572dc9df4b59",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/5f0764cb1c81a9712bce605d38efe6d844a70b29",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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{
"url": "https://git.kernel.org/stable/c/aa480f05aed7a9eee87d4a6fc90647fe9679c670",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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{
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"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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],
"vulnStatus": "Received",
"descriptions": [
{
"lang": "en",
"value": "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_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."
}
],
"lastModified": "2026-10-19T10:19:49.290",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}