CVE-2026-63828 (GCVE-0-2026-63828)
Vulnerability from cvelistv5
Published
2026-07-19 12:02
Modified
2026-08-17 04:51
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
apparmor: mediate the implicit connect of TCP fast open sendmsg
sendmsg()/sendto() with MSG_FASTOPEN is a combination of connect(2) and
write(2): it opens the connection in the SYN. apparmor_socket_sendmsg()
only checks AA_MAY_SEND, so a profile that grants send but denies connect
lets a confined task open an outbound TCP/MPTCP connection that connect(2)
would have refused, bypassing connect mediation.
Mediate the implicit connect when MSG_FASTOPEN is set and a destination
is supplied. Add it to apparmor_socket_sendmsg() (not the shared
aa_sock_msg_perm() helper, which recvmsg also uses) and call aa_sk_perm()
directly, mirroring the selinux and tomoyo fixes. sk_is_tcp() does not
cover MPTCP fast open, so the SOCK_STREAM/IPPROTO_MPTCP arm is explicit.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: cf60af03ca4e71134206809ea892e49b92a88896 Version: cf60af03ca4e71134206809ea892e49b92a88896 Version: cf60af03ca4e71134206809ea892e49b92a88896 Version: cf60af03ca4e71134206809ea892e49b92a88896 Version: cf60af03ca4e71134206809ea892e49b92a88896 Version: cf60af03ca4e71134206809ea892e49b92a88896 Version: cf60af03ca4e71134206809ea892e49b92a88896 Version: cf60af03ca4e71134206809ea892e49b92a88896 |
||
{
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{
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{
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"status": "unaffected",
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{
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"version": "7.1.3",
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{
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"status": "unaffected",
"version": "7.2",
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\napparmor: mediate the implicit connect of TCP fast open sendmsg\n\nsendmsg()/sendto() with MSG_FASTOPEN is a combination of connect(2) and\nwrite(2): it opens the connection in the SYN. apparmor_socket_sendmsg()\nonly checks AA_MAY_SEND, so a profile that grants send but denies connect\nlets a confined task open an outbound TCP/MPTCP connection that connect(2)\nwould have refused, bypassing connect mediation.\n\nMediate the implicit connect when MSG_FASTOPEN is set and a destination\nis supplied. Add it to apparmor_socket_sendmsg() (not the shared\naa_sock_msg_perm() helper, which recvmsg also uses) and call aa_sk_perm()\ndirectly, mirroring the selinux and tomoyo fixes. sk_is_tcp() does not\ncover MPTCP fast open, so the SOCK_STREAM/IPPROTO_MPTCP arm is explicit."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 8.4,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - Exploitation requires a confined local process to invoke sendmsg(2)/sendto(2) with MSG_FASTOPEN; the vulnerable AppArmor LSM hook runs on the syscall path before TCP fast-open performs its implicit connect.\nAC:L - Any confined task that already has send permission can reliably trigger the bypass with a single sendmsg/sendto call using MSG_FASTOPEN and a destination address, with no race or special victim state required beyond TCP Fast Open client support.\nPR:L - The attacker must be an unprivileged process confined by an AppArmor profile that grants network send but denies connect (e.g., hardened Snap/sandboxed service profiles on Ubuntu); no real root or capabilities beyond normal confined-user execution are needed.\nUI:N - No victim interaction is required; the confined attacker process directly issues the bypassing syscall without needing another user or administrator to perform any action.\nS:C - Successful exploitation crosses the AppArmor confinement boundary, allowing a sandboxed task to establish outbound TCP/MPTCP connections that connect(2) mediation would have blocked, escaping the intended network policy scope.\nC:H - Bypassing connect mediation lets a confined process open TCP/MPTCP sessions to destinations policy forbids and read arbitrary response data from those services (internal APIs, metadata endpoints, C2 servers), constituting unauthorized information disclosure.\nI:H - The bypass enables unauthorized outbound connection establishment and transmission of arbitrary application data (including SYN-cookie data) to hosts explicitly denied by the AppArmor connect rule, violating integrity of the confinement policy.\nA:N - This is a pure LSM policy-bypass flaw with no kernel memory corruption, panic, oops, hang, or resource exhaustion; exploitation does not impact system availability."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-17T04:51:36.839Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/a16714e7cf2baa98ba2efddd5d6cbac641f4e76b"
},
{
"url": "https://git.kernel.org/stable/c/20383429b56974507c465d016e5238b189f7a246"
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{
"url": "https://git.kernel.org/stable/c/7f57428ce00891d26b0f087ef754a4d820ec83aa"
},
{
"url": "https://git.kernel.org/stable/c/faea60deaa05c76f0772650f42eafde12bd39d93"
},
{
"url": "https://git.kernel.org/stable/c/07b71c342382b854ab8030b244aeab6a7228ad7d"
},
{
"url": "https://git.kernel.org/stable/c/4a69b83045d3195d5b9a9b053ad840ddb2998b4e"
},
{
"url": "https://git.kernel.org/stable/c/45ebb934ea50b436ce49b2f159f090dab0d7fa28"
},
{
"url": "https://git.kernel.org/stable/c/4d587cd8a72155089a627130bbd4716ec0856e21"
}
],
"title": "apparmor: mediate the implicit connect of TCP fast open sendmsg",
"x_generator": {
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},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-63828",
"datePublished": "2026-07-19T12:02:22.644Z",
"dateReserved": "2026-07-19T07:54:57.014Z",
"dateUpdated": "2026-08-17T04:51:36.839Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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