CVE-2026-74478 (GCVE-0-2026-74478)
Vulnerability from cvelistv5
Published
2026-08-15 12:27
Modified
2026-08-19 16:37
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
um: vector: fix use-after-free in vector_mmsg_rx()
When vector_mmsg_rx() discards a packet whose overlay header fails
verify_header(), it frees the skb and continues the loop:
if (header_check < 0) {
dev_kfree_skb_irq(skb);
vp->estats.rx_encaps_errors++;
continue;
}
The normal and short-packet paths fall through to the bottom of the
loop body, which clears the consumed slot and advances the cursors:
(*skbuff_vector) = NULL;
mmsg_vector++;
skbuff_vector++;
The verify_header() < 0 path skips that via continue, so the freed skb
is left in skbuff_vector[] and the cursors do not advance. The next
iteration reads the same slot, gets the freed skb, and frees it again,
producing a refcount underflow / use-after-free in the RX path.
Discard the slot the same way the other paths do before continuing.
Only transports whose verify_header() can return negative are affected:
GRE and L2TPv3 do so on a cookie/session-id mismatch (raw/tap do not),
so any peer on such a transport can trigger it without authentication.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: 49da7e64f33e80edffb1a9eeb230fa4c3f42dffb Version: 49da7e64f33e80edffb1a9eeb230fa4c3f42dffb Version: 49da7e64f33e80edffb1a9eeb230fa4c3f42dffb Version: 49da7e64f33e80edffb1a9eeb230fa4c3f42dffb Version: 49da7e64f33e80edffb1a9eeb230fa4c3f42dffb Version: 49da7e64f33e80edffb1a9eeb230fa4c3f42dffb Version: 49da7e64f33e80edffb1a9eeb230fa4c3f42dffb Version: 49da7e64f33e80edffb1a9eeb230fa4c3f42dffb |
||
{
"containers": {
"cna": {
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"product": "Linux",
"programFiles": [
"arch/um/drivers/vector_kern.c"
],
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"vendor": "Linux",
"versions": [
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"version": "4.17"
},
{
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"status": "unaffected",
"version": "0",
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{
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"status": "unaffected",
"version": "5.10.265",
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},
{
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"status": "unaffected",
"version": "5.15.216",
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},
{
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"version": "6.1.183",
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{
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"version": "6.6.151",
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},
{
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{
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"status": "unaffected",
"version": "7.1.8",
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},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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},
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{
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}
],
"negate": false,
"operator": "OR"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\num: vector: fix use-after-free in vector_mmsg_rx()\n\nWhen vector_mmsg_rx() discards a packet whose overlay header fails\nverify_header(), it frees the skb and continues the loop:\n\n\tif (header_check \u003c 0) {\n\t\tdev_kfree_skb_irq(skb);\n\t\tvp-\u003eestats.rx_encaps_errors++;\n\t\tcontinue;\n\t}\n\nThe normal and short-packet paths fall through to the bottom of the\nloop body, which clears the consumed slot and advances the cursors:\n\n\t(*skbuff_vector) = NULL;\n\tmmsg_vector++;\n\tskbuff_vector++;\n\nThe verify_header() \u003c 0 path skips that via continue, so the freed skb\nis left in skbuff_vector[] and the cursors do not advance. The next\niteration reads the same slot, gets the freed skb, and frees it again,\nproducing a refcount underflow / use-after-free in the RX path.\n\nDiscard the slot the same way the other paths do before continuing.\n\nOnly transports whose verify_header() can return negative are affected:\nGRE and L2TPv3 do so on a cookie/session-id mismatch (raw/tap do not),\nso any peer on such a transport can trigger it without authentication."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:N - The bug is reached from remotely sent GRE or L2TPv3 packets processed by vector_mmsg_rx() via recvmmsg on the tunnel socket; the fix commit states any peer on those transports can trigger it without authentication.\nAC:L - An attacker reliably triggers verify_header() failure with a wrong GRE key or L2TPv3 session/cookie, and sending two or more malformed packets in one recvmmsg batch causes immediate double-free of the same skb without races or special memory layout.\nPR:N - No privileges on the UML instance are required; exploitation needs only the ability to send network packets on the configured GRE/L2TPv3 transport, and overlay keys/cookies are not authenticated security controls.\nUI:N - Exploitation is driven entirely by remote packets delivered to the vector netdev RX path and requires no victim user or administrator action beyond the interface already being up.\nS:U - The use-after-free corrupts sk_buff memory inside the UML kernel network driver and does not by itself cross a VM, IOMMU, or host-kernel security boundary.\nC:H - The refcount underflow/use-after-free leaves a dangling sk_buff pointer that can be reallocated and read through standard heap grooming, giving an arbitrary kernel memory disclosure primitive.\nI:H - Reclaiming the freed sk_buff enables attacker-controlled contents in kernel heap objects and can be leveraged for arbitrary write or control-flow hijack in the UML kernel context.\nA:H - The double-free in the RX path can immediately oops or panic the UML kernel, and an unauthenticated remote peer can retrigger the condition by sending additional malformed tunnel packets."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-19T16:37:30.555Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/967c779c9853d2a1cc9cd8e61d300250c348f3d9"
},
{
"url": "https://git.kernel.org/stable/c/a7bc015bb798c525e7a82dd14225c6aeb994274b"
},
{
"url": "https://git.kernel.org/stable/c/7dc9781e320d664c9bdd50003c9acfddf363d1e1"
},
{
"url": "https://git.kernel.org/stable/c/4b9601595e8b6b5d18878cac0aeabc687d241111"
},
{
"url": "https://git.kernel.org/stable/c/67d58ab4f2ccf7145f3da07e025735a09c79de1b"
},
{
"url": "https://git.kernel.org/stable/c/180ff4c81faf01ec4e06082c9daa7c40518ead89"
},
{
"url": "https://git.kernel.org/stable/c/804b681002ead233abf49a3efd681f5468a835f9"
},
{
"url": "https://git.kernel.org/stable/c/af421e9aed3920c7ac88c24daa48606c7112feca"
}
],
"title": "um: vector: fix use-after-free in vector_mmsg_rx()",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-74478",
"datePublished": "2026-08-15T12:27:12.549Z",
"dateReserved": "2026-08-15T05:44:03.903Z",
"dateUpdated": "2026-08-19T16:37:30.555Z",
"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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