CVE-2026-74496 (GCVE-0-2026-74496)
Vulnerability from cvelistv5 – Published: 2026-08-15 12:27 – Updated: 2026-09-21 13:14
VLAI
EPSS
VEX
Title
fou: Fix use-after-free in fou_create()
Summary
In the Linux kernel, the following vulnerability has been resolved:
fou: Fix use-after-free in fou_create()
fou_create() publishes struct fou through sk_user_data before adding the
new FOU port to the per-netns list. If fou_add_to_port_list() fails,
the error path frees fou while it is still reachable through
sk_user_data. A concurrent receive can then dereference the freed
object in fou_from_sock().
This ordering issue was previously noted in the linked discussion.
The failure is reachable when local port 0 is requested. Each socket
binds to a different ephemeral port, but fou_cfg_cmp() compares the
requested port 0 and reports -EALREADY once an entry already exists.
Release the tunnel socket before freeing fou so sk_user_data is cleared
first, and defer reclamation with kfree_rcu() to protect concurrent RCU
readers. This matches the lifetime handling in fou_release().
Severity
7.8 (High)
Assigner
References
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
23461551c00628c3f3fe9cf837bf53cf8f212b63 , < 58835985c035a8333742f829ad7e0889a082f9d3
(git)
Affected: 23461551c00628c3f3fe9cf837bf53cf8f212b63 , < 9042867d4701728f0c6527215b11471759904d8f (git) Affected: 23461551c00628c3f3fe9cf837bf53cf8f212b63 , < a28d8903bfe76089ea4bbdbff9976965f9ef8107 (git) Affected: 23461551c00628c3f3fe9cf837bf53cf8f212b63 , < b14361aca6350ff7907b0e9903c7b94dc7d5d4a0 (git) |
guessed | |
| Linux | Linux |
Affected:
3.18
Unaffected: 0 , < 3.18 (semver) Unaffected: 6.12.111 , ≤ 6.12.* (semver) Unaffected: 6.18.53 , ≤ 6.18.* (semver) Unaffected: 7.1.8 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix) |
guessed |
{
"containers": {
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"product": "Linux",
"programFiles": [
"net/ipv4/fou_core.c"
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"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "3.18"
},
{
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"status": "unaffected",
"version": "0",
"versionType": "semver"
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{
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"status": "unaffected",
"version": "6.12.111",
"versionType": "semver"
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{
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"status": "unaffected",
"version": "6.18.53",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.1.*",
"status": "unaffected",
"version": "7.1.8",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
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"versionEndExcluding": "6.12.111",
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{
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}
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"negate": false,
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"descriptions": [
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"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfou: Fix use-after-free in fou_create()\n\nfou_create() publishes struct fou through sk_user_data before adding the\nnew FOU port to the per-netns list. If fou_add_to_port_list() fails,\nthe error path frees fou while it is still reachable through\nsk_user_data. A concurrent receive can then dereference the freed\nobject in fou_from_sock().\n\nThis ordering issue was previously noted in the linked discussion.\n\nThe failure is reachable when local port 0 is requested. Each socket\nbinds to a different ephemeral port, but fou_cfg_cmp() compares the\nrequested port 0 and reports -EALREADY once an entry already exists.\n\nRelease the tunnel socket before freeing fou so sk_user_data is cleared\nfirst, and defer reclamation with kfree_rcu() to protect concurrent RCU\nreaders. This matches the lifetime handling in fou_release()."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - The UAF is opened only via local FOU_CMD_ADD genetlink into fou_create(); remote UDP can race the dangling sk_user_data read in fou_udp_recv/gue_udp_recv but cannot alone reach the erroneous teardown path.\nAC:L - An attacker with CAP_NET_ADMIN controls both sides: issue a second FOU_CMD_ADD with port 0 to force -EALREADY on fou_add_to_port_list while concurrently sending UDP/GRO traffic to the just-bound ephemeral socket during the kfree window.\nPR:L - FOU_CMD_ADD is gated by GENL_ADMIN_PERM (CAP_NET_ADMIN); the fou genl family is netnsok, so a user with CAP_NET_ADMIN inside unshare -Urn can configure FOU and trigger the failing add path without init-namespace root.\nUI:N - Exploitation is fully programmatic via concurrent netlink FOU_CMD_ADD requests and attacker-controlled UDP packets; no victim mount, file open, or other interactive action is required.\nS:U - Impact is kernel heap corruption and privilege escalation within the same security authority; this is not a VM escape, IOMMU bypass, or other cross-boundary scope change.\nC:H - Concurrent readers call fou_from_sock() and dereference freed struct fou fields (family, protocol, flags); reclaimed slab contents give attacker-controlled reads and kernel pointer disclosure primitives typical of UAF.\nI:H - Freed struct fou is attacker-reclaimable kmalloc memory; fou_gro_receive indexes inet_offloads[fou-\u003eprotocol] from the dangling pointer, enabling heap grooming for arbitrary writes and control-flow hijack.\nA:H - Use-after-free in UDP receive/GRO softirq reliably causes KASAN violations and, on production kernels, invalid pointer dereferences or panics when accessing the freed fou object during packet processing."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-09-21T13:14:05.619Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/58835985c035a8333742f829ad7e0889a082f9d3"
},
{
"url": "https://git.kernel.org/stable/c/9042867d4701728f0c6527215b11471759904d8f"
},
{
"url": "https://git.kernel.org/stable/c/a28d8903bfe76089ea4bbdbff9976965f9ef8107"
},
{
"url": "https://git.kernel.org/stable/c/b14361aca6350ff7907b0e9903c7b94dc7d5d4a0"
}
],
"title": "fou: Fix use-after-free in fou_create()",
"x_generator": {
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"cveMetadata": {
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"assignerShortName": "Linux",
"cveId": "CVE-2026-74496",
"datePublished": "2026-08-15T12:27:23.854Z",
"dateReserved": "2026-08-15T05:44:03.906Z",
"dateUpdated": "2026-09-21T13:14:05.619Z",
"state": "PUBLISHED"
},
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"epss": {
"cve": "CVE-2026-74496",
"date": "2026-10-01",
"epss": "0.00125",
"percentile": "0.01905"
},
"microsoft_vex": {
"current_release_date": "2026-09-23T02:57:03.000Z",
"cve": "CVE-2026-74496",
"id": "msrc_CVE-2026-74496",
"initial_release_date": "2026-08-23T14:46:12.000Z",
"product_status:known_affected": "2",
"source": "Microsoft CSAF VEX",
"status": "final",
"title": "fou: Fix use-after-free in fou_create()",
"url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-74496.json",
"version": "2"
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"product": "Linux",
"programFiles": [
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"vendor": "Linux",
"versions": [
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"version": "3.18"
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"status": "unaffected",
"version": "0",
"versionType": "semver"
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"versionType": "semver"
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},
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"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"cveTags": [],
"descriptions": [
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"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfou: Fix use-after-free in fou_create()\n\nfou_create() publishes struct fou through sk_user_data before adding the\nnew FOU port to the per-netns list. If fou_add_to_port_list() fails,\nthe error path frees fou while it is still reachable through\nsk_user_data. A concurrent receive can then dereference the freed\nobject in fou_from_sock().\n\nThis ordering issue was previously noted in the linked discussion.\n\nThe failure is reachable when local port 0 is requested. Each socket\nbinds to a different ephemeral port, but fou_cfg_cmp() compares the\nrequested port 0 and reports -EALREADY once an entry already exists.\n\nRelease the tunnel socket before freeing fou so sk_user_data is cleared\nfirst, and defer reclamation with kfree_rcu() to protect concurrent RCU\nreaders. This matches the lifetime handling in fou_release()."
}
],
"id": "CVE-2026-74496",
"lastModified": "2026-09-21T14:17:19.223",
"metrics": {
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"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7.8,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"exploitabilityScore": 1.8,
"impactScore": 5.9,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
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"published": "2026-08-15T13:17:54.557",
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"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Received"
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},
"redhat_vex": {
"aggregate_severity": "Moderate",
"current_release_date": "2026-08-21T07:57:43+00:00",
"cve": "CVE-2026-74496",
"id": "CVE-2026-74496",
"initial_release_date": "2026-08-15T00:00:00+00:00",
"product_status:known_affected": "184",
"product_status:known_not_affected": "90",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: fou: Fix use-after-free in fou_create()",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74496.json",
"version": "3"
},
"suse_vex": {
"aggregate_severity": "important",
"current_release_date": "2026-09-24T16:29:16Z",
"cve": "CVE-2026-74496",
"id": "CVE-2026-74496",
"initial_release_date": "2026-08-21T00:40:43Z",
"product_status:first_fixed": "164",
"product_status:known_affected": "603",
"product_status:known_not_affected": "4",
"product_status:recommended": "282",
"source": "SUSE CSAF VEX",
"status": "interim",
"title": "SUSE CVE CVE-2026-74496",
"url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-74496.json",
"version": "14"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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