CVE-2026-56857 (GCVE-0-2026-56857)
Vulnerability from cvelistv5 – Published: 2026-10-08 22:53 – Updated: 2026-10-09 15:36
VLAI
EPSS
VEX
Title
Root.Mkdir(All) can follow junctions out of the root on Windows in os
Summary
On Windows, when the target of Root.Mkdir or Root.MkdirAll is a junction pointing to an empty location, the operation can create a directory at the junction target even when that target is located outside the root. This only applies to operations where the last path component is a junction (path/to/junction, but not path/junction/target).
Severity
9.8 (Critical)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-09 15:35 UTC
CWE
- CWE-1386 - Insecure Operation on Windows Junction / Mount Point
Assigner
References
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Go standard library | os |
Affected:
0 , < 1.26.9
(semver)
Affected: 1.27.0-0 , < 1.27.2 (semver) |
guessed | |
| Go standard library | internal/syscall/windows |
Affected:
0 , < 1.26.9
(semver)
Affected: 1.27.0-0 , < 1.27.2 (semver) |
guessed |
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}
]
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"title": "CISA ADP Vulnrichment"
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],
"cna": {
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{
"collectionURL": "https://pkg.go.dev",
"defaultStatus": "unaffected",
"packageName": "os",
"platforms": [
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],
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"programRoutines": [
{
"name": "Root.Mkdir"
},
{
"name": "doInRoot"
},
{
"name": "rootMkdirAll"
},
{
"name": "Root.Chmod"
},
{
"name": "Root.Chown"
},
{
"name": "Root.Chtimes"
},
{
"name": "Root.Lchown"
},
{
"name": "Root.Link"
},
{
"name": "Root.MkdirAll"
},
{
"name": "Root.Remove"
},
{
"name": "Root.RemoveAll"
},
{
"name": "Root.Rename"
},
{
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}
],
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}
]
},
{
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"defaultStatus": "unaffected",
"packageName": "internal/syscall/windows",
"platforms": [
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],
"product": "internal/syscall/windows",
"programRoutines": [
{
"name": "Mkdirat"
}
],
"vendor": "Go standard library",
"versions": [
{
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"status": "affected",
"version": "0",
"versionType": "semver"
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{
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"status": "affected",
"version": "1.27.0-0",
"versionType": "semver"
}
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}
],
"credits": [
{
"lang": "en",
"value": "Daniele Ballarini"
}
],
"descriptions": [
{
"lang": "en",
"value": "On Windows, when the target of Root.Mkdir or Root.MkdirAll is a junction pointing to an empty location, the operation can create a directory at the junction target even when that target is located outside the root. This only applies to operations where the last path component is a junction (path/to/junction, but not path/junction/target)."
}
],
"problemTypes": [
{
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{
"description": "CWE-1386: Insecure Operation on Windows Junction / Mount Point",
"lang": "en"
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"orgId": "1bb62c36-49e3-4200-9d77-64a1400537cc",
"shortName": "Go"
},
"references": [
{
"url": "https://go.dev/cl/847305"
},
{
"url": "https://go.dev/issue/81739"
},
{
"url": "https://groups.google.com/g/golang-announce/c/U2fTuyDJznI"
},
{
"url": "https://pkg.go.dev/vuln/GO-2026-6604"
}
],
"title": "Root.Mkdir(All) can follow junctions out of the root on Windows in os"
}
},
"cveMetadata": {
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"assignerShortName": "Go",
"cveId": "CVE-2026-56857",
"datePublished": "2026-10-08T22:53:58.387Z",
"dateReserved": "2026-06-23T15:10:49.353Z",
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"state": "PUBLISHED"
},
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"dataVersion": "5.2",
"vulnerability-lookup:meta": {
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"date": "2026-11-01",
"epss": "0.00553",
"percentile": "0.46225"
},
"microsoft_vex": {
"current_release_date": "2026-10-16T01:51:20.000Z",
"cve": "CVE-2026-56857",
"id": "msrc_CVE-2026-56857",
"initial_release_date": "2026-10-11T01:54:56.000Z",
"product_status:known_not_affected": "2",
"source": "Microsoft CSAF VEX",
"status": "final",
"title": "Root.Mkdir(All) can follow junctions out of the root on Windows in os",
"url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-56857.json",
"version": "3"
},
"nvd": {
"cve": {
"affected": [
{
"affectedData": [
{
"collectionURL": "https://pkg.go.dev",
"defaultStatus": "unaffected",
"packageName": "os",
"platforms": [
"windows"
],
"product": "os",
"programRoutines": [
{
"name": "Root.Mkdir"
},
{
"name": "doInRoot"
},
{
"name": "rootMkdirAll"
},
{
"name": "Root.Chmod"
},
{
"name": "Root.Chown"
},
{
"name": "Root.Chtimes"
},
{
"name": "Root.Lchown"
},
{
"name": "Root.Link"
},
{
"name": "Root.MkdirAll"
},
{
"name": "Root.Remove"
},
{
"name": "Root.RemoveAll"
},
{
"name": "Root.Rename"
},
{
"name": "Root.Symlink"
}
],
"vendor": "Go standard library",
"versions": [
{
"lessThan": "1.26.9",
"status": "affected",
"version": "0",
"versionType": "semver"
},
{
"lessThan": "1.27.2",
"status": "affected",
"version": "1.27.0-0",
"versionType": "semver"
}
]
},
{
"collectionURL": "https://pkg.go.dev",
"defaultStatus": "unaffected",
"packageName": "internal/syscall/windows",
"platforms": [
"windows"
],
"product": "internal/syscall/windows",
"programRoutines": [
{
"name": "Mkdirat"
}
],
"vendor": "Go standard library",
"versions": [
{
"lessThan": "1.26.9",
"status": "affected",
"version": "0",
"versionType": "semver"
},
{
"lessThan": "1.27.2",
"status": "affected",
"version": "1.27.0-0",
"versionType": "semver"
}
]
}
],
"source": "security@golang.org"
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "On Windows, when the target of Root.Mkdir or Root.MkdirAll is a junction pointing to an empty location, the operation can create a directory at the junction target even when that target is located outside the root. This only applies to operations where the last path component is a junction (path/to/junction, but not path/junction/target)."
}
],
"id": "CVE-2026-56857",
"lastModified": "2026-10-09T16:35:35.900",
"metrics": {
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"attackVector": "NETWORK",
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"baseScore": 9.8,
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"confidentialityImpact": "HIGH",
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"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
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"impactScore": 5.9,
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"type": "Secondary"
}
],
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},
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"timestamp": "2026-10-09T15:35:58.663117Z",
"version": "2.0.3"
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"published": "2026-10-08T23:17:01.487",
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},
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"url": "https://groups.google.com/g/golang-announce/c/U2fTuyDJznI"
},
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"url": "https://pkg.go.dev/vuln/GO-2026-6604"
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],
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"current_release_date": "2026-10-30T18:54:53+00:00",
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"product_status:fixed": "80",
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"source": "Red Hat CSAF VEX",
"status": "final",
"title": "os: golang: golang: Directory traversal via Windows junction handling",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-56857.json",
"version": "3"
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{
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{
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{
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{
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}
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},
{
"url": "https://pkg.go.dev/vuln/GO-2026-6604"
}
],
"title": "Root.Mkdir(All) can follow junctions out of the root on Windows in os"
}
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}
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
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They have not been verified by an analyst and are provided for guidance only.
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Browse all ATT&CK techniques and the vulnerabilities related to each.
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