ipv6: seg6: clear IPv4 control block on IPIP decapsulation
In the Linux kernel, the following vulnerability has been resolved: ipv6: seg6: clear IPv4 control block on IPIP decapsulation End.DX4 and End.DT4 decapsulate an IPv4 packet through decap_and_validate() and send it directly to IPv4 routing. The inner packet therefore bypasses ip_rcv_core(), which normally clears IPCB before IPv4 interprets skb->cb. The skb instead retains IP6CB data from the outer packet. IP6CB and IPCB use the same skb->cb storage, so IP6CB(skb)->lastopt overlaps IPCB(skb)->opt.optlen and srr, while IP6CB(skb)->nhoff overlaps rr and ts. The sender can make the stale optlen byte nonzero with a valid outer extension-header chain. The reproducers put an eight-byte Destination Options header immediately after the 40-byte IPv6 header and before the Segment Routing Header. ipv6_destopt_rcv() records the sender-controlled Destination Options offset in both lastopt and nhoff, setting them to 40. On the reproduced little-endian x86-64 kernel, IPv4 therefore sees optlen = 40 and rr = 40. Both tcp_v4_save_options() and __ip_options_echo() skip option copying when optlen is zero. Here optlen is 40, so the TCP SYN path allocates room for 40 bytes of option data and calls __ip_options_echo(). The stale rr value makes that function read inner packet byte 41 as the Record Route option length. The reproducers set that sender-controlled byte to 255, so __ip_options_echo() copies 255 bytes into the 40-byte option-data area. Separate End.DX4 and End.DT4 reproducers on the unpat
CVE-2026-80840
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: cve:CVE-2026-80840
Linux
Source reference: /containers/cna/affected/0/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Linux
Source reference: /containers/cna/affected/1/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556",
"lessThan": "10fd1a8f58ac619a9e251f2858e2e2c8fd6cd667",
"versionType": "git"
},
{
"status": "affected",
"version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556",
"lessThan": "eb0f422487228e140f3d609b032ac61aedcab8fa",
"versionType": "git"
},
{
"status": "affected",
"version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556",
"lessThan": "9039e4f3e1c0ffe2b575b655b3f58fdd10f7e40c",
"versionType": "git"
},
{
"status": "affected",
"version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556",
"lessThan": "f52f1e75716d2ee49e013edf204ac92337c72fd8",
"versionType": "git"
},
{
"status": "affected",
"version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556",
"lessThan": "0e3f01fe2e704e76af4385b8a1742641885a191c",
"versionType": "git"
},
{
"status": "affected",
"version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556",
"lessThan": "3e4476e58343fb8f2fffced9e22d935376b17aaf",
"versionType": "git"
},
{
"status": "affected",
"version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556",
"lessThan": "bf1c1151560d11036a144d917fa4c131831342d7",
"versionType": "git"
},
{
"status": "affected",
"version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556",
"lessThan": "f4be3b391265e24c7720fc867c50062b436acf33",
"versionType": "git"
},
{
"status": "affected",
"version": "891ef8dd2a8d14e4e73a81dcdb135b574c57f556",
"lessThan": "44930446dde45a7a90fe1446fa38eb0e2c561646",
"versionType": "git"
}
],
"programFiles": [
"net/ipv6/seg6_local.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "4.14"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "4.14",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "5.10.269",
"versionType": "semver",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.220",
"versionType": "semver",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "6.1.187",
"versionType": "semver",
"lessThanOrEqual": "6.1.*"
},
{
"status": "unaffected",
"version": "6.6.156",
"versionType": "semver",
"lessThanOrEqual": "6.6.*"
},
{
"status": "unaffected",
"version": "6.12.108",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.49",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.1.13",
"versionType": "semver",
"lessThanOrEqual": "7.1.*"
},
{
"status": "unaffected",
"version": "7.2.3",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"net/ipv6/seg6_local.c"
],
"defaultStatus": "affected"
}
]- Related CVEs
- CVE-2026-80840
Source reference:
/cveMetadata/cveId
Publisher severity
No explicit severity was provided.
- Event
- #34856 · Revision 1
- Added to Heist Feed
- Publisher date