Critical
node-flatted — security advisory
flatted is a circular JSON parser. Prior to version 3.4.2, the parse() function in flatted can use attacker-controlled string values from the parsed JSON as direct array index keys, without validating that they are numeric. Since the internal input buffer is a JavaScript Array, accessing it with the key "__proto__" returns Array.prototype via the inherited getter. This object is then treated as a legitimate parsed value and assigned as a property of the output object, effectively leaking a live reference to Array.prototype to the consumer. Any code that subsequently writes to that property will pollute the global prototype. This issue has been patched in version 3.4.2.
- Products
- node-flatted
- Affected versions
- 2.0.1~dfsg-3, 2.0.1~dfsg-4, 2.0.2~dfsg-1, 2.0.2~dfsg-4, 3.2.2~ds-2, 3.2.2~ds-3, 3.2.4~ds-1, 3.2.5~ds-1, 3.2.7~ds-1, 3.4.2~ds-1, 3.4.4~ds-1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-33228
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 02:59 UTC · Revision 1
Source evidence
flatted is a circular JSON parser. Prior to version 3.4.2, the parse() function in flatted can use attacker-controlled string values from the parsed JSON as direct array index keys, without validating that they are numeric. Since the internal input buffer is a JavaScript Array, accessing it with the key "__proto__" returns Array.prototype via the inherited getter. This object is then treated as a legitimate parsed value and assigned as a property of the output object, effectively leaking a live reference to Array.prototype to the consumer. Any code that subsequently writes to that property will pollute the global prototype. This issue has been patched in version 3.4.2.
osv:UBUNTU-CVE-2026-33228
node-flatted
Fixed versions: Not specified
node-flatted
Fixed versions: Not specified
node-flatted
Fixed versions: Not specified
node-flatted
Fixed versions: Not specified
node-flatted
Fixed versions: Not specified
node-flatted
Fixed versions: Not specified
Complete source record
{
"id": "a4d512ad740edeb302aaca2ac6709c0ecdc0fb0d740d052e5a3ca443ff819884",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-33228",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-33228",
"summary": "flatted is a circular JSON parser. Prior to version 3.4.2, the parse() function in flatted can use attacker-controlled string values from the parsed JSON as direct array index keys, without validating that they are numeric. Since the internal input buffer is a JavaScript Array, accessing it with the key \"__proto__\" returns Array.prototype via the inherited getter. This object is then treated as a legitimate parsed value and assigned as a property of the output object, effectively leaking a live reference to Array.prototype to the consumer. Any code that subsequently writes to that property will pollute the global prototype. This issue has been patched in version 3.4.2.",
"evidence": "osv:UBUNTU-CVE-2026-33228",
"products": [
{
"name": {
"value": "node-flatted",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "2.0.1~dfsg-3",
"evidence": "/affected/0/versions"
},
{
"value": "2.0.1~dfsg-4",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "node-flatted",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
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"affected_versions": [
{
"value": "2.0.2~dfsg-1",
"evidence": "/affected/1/versions"
},
{
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"evidence": "/affected/1/versions"
},
{
"value": "3.2.2~ds-2",
"evidence": "/affected/1/versions"
},
{
"value": "3.2.2~ds-3",
"evidence": "/affected/1/versions"
},
{
"value": "3.2.4~ds-1",
"evidence": "/affected/1/versions"
},
{
"value": "3.2.5~ds-1",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
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"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.2.7~ds-1",
"evidence": "/affected/2/versions"
}
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},
{
"name": {
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"evidence": "/affected/3/package/name"
},
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"affected_versions": [
{
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"evidence": "/affected/3/versions"
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},
{
"name": {
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"evidence": "/affected/4/package/name"
},
"prerequisites": [],
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"affected_versions": [
{
"value": "3.4.2~ds-1",
"evidence": "/affected/4/versions"
},
{
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"evidence": "/affected/4/versions"
}
]
},
{
"name": {
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"evidence": "/affected/5/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.2.7~ds-1",
"evidence": "/affected/5/versions"
},
{
"value": "3.4.2~ds-1",
"evidence": "/affected/5/versions"
}
]
}
],
"severity": "critical",
"structured": {
"id": "UBUNTU-CVE-2026-33228",
"aliases": [
"UBUNTU-CVE-2026-33228"
],
"metrics": [
{
"type": "CVSS_V4",
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P"
},
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
},
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
},
{
"type": "Ubuntu",
"score": "medium"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "node-flatted",
"purl": "pkg:deb/ubuntu/node-flatted?arch=source&distro=focal",
"ecosystem": "Ubuntu:20.04:LTS"
},
"versions": [
"2.0.1~dfsg-3",
"2.0.1~dfsg-4"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33228.json"
},
"ecosystem_specific": {
"binaries": [
{
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"binary_version": "2.0.1~dfsg-4"
},
{
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{
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}
],
"package": {
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"purl": "pkg:deb/ubuntu/node-flatted?arch=source&distro=jammy",
"ecosystem": "Ubuntu:22.04:LTS"
},
"versions": [
"2.0.2~dfsg-1",
"2.0.2~dfsg-4",
"3.2.2~ds-2",
"3.2.2~ds-3",
"3.2.4~ds-1",
"3.2.5~ds-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33228.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libjs-flatted",
"binary_version": "3.2.5~ds-1"
},
{
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}
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}
},
{
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"events": [
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"introduced": "0"
}
]
}
],
"package": {
"name": "node-flatted",
"purl": "pkg:deb/ubuntu/node-flatted?arch=source&distro=noble",
"ecosystem": "Ubuntu:24.04:LTS"
},
"versions": [
"3.2.7~ds-1"
],
"database_specific": {
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},
"ecosystem_specific": {
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},
{
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"package": {
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"purl": "pkg:deb/ubuntu/node-flatted?arch=source&distro=questing",
"ecosystem": "Ubuntu:25.10"
},
"versions": [
"3.2.7~ds-1"
],
"database_specific": {
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"ecosystem_specific": {
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],
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},
"ecosystem_specific": {
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},
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},
{
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"purl": "pkg:deb/ubuntu/node-flatted?arch=source&distro=resolute",
"ecosystem": "Ubuntu:26.04:LTS"
},
"versions": [
"3.2.7~ds-1",
"3.4.2~ds-1"
],
"database_specific": {
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},
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],
"modified": "2026-10-17T13:00:00.022615447Z",
"provider": "osv",
"upstream": [
"CVE-2026-33228"
],
"references": [
"https://ubuntu.com/security/CVE-2026-33228",
"https://www.cve.org/CVERecord?id=CVE-2026-33228",
"https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802",
"https://github.com/WebReflection/flatted/releases/tag/v3.4.2",
"https://github.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjgh"
]
},
"related_cves": [
{
"value": "CVE-2026-33228",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/1/score"
},
"source_id": "core-osv",
"document_id": 360095,
"published_at": "2026-03-20T23:16:00+00:00"
}