js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources
js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 until 3.15.2, 4.3.2, and 5.4.1, maxTotalMergeKeys in lib/js-yaml/loader.js and lib/loader.js does not count empty mapping sources while processing the merge key <<. An attacker can alias a large sequence of empty mappings into many merge targets, causing O(N * K) processing while totalMergeKeys remains unchanged and the configured resource limit is never reached. A relatively small YAML document can therefore cause prolonged CPU consumption in applications that parse untrusted YAML, and merge processing is enabled by default on these release lines. In v3 & v4, merge is enabled by default so the severity score is higher. This issue is fixed in versions 3.15.2, 4.3.2, and 5.4.1.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-84375
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 4 Nov 2026, 02:19 UTC · Revision 1
Source evidence
js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources
core-osv · Original sourcePublished 1 Sept 2026, 21:43 UTC
js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 until 3.15.2, 4.3.2, and 5.4.1, maxTotalMergeKeys in lib/js-yaml/loader.js and lib/loader.js does not count empty mapping sources while processing the merge key <<. An attacker can alias a large sequence of empty mappings into many merge targets, causing O(N * K) processing while totalMergeKeys remains unchanged and the configured resource limit is never reached. A relatively small YAML document can therefore cause prolonged CPU consumption in applications that parse untrusted YAML, and merge processing is enabled by default on these release lines. In v3 & v4, merge is enabled by default so the severity score is higher. This issue is fixed in versions 3.15.2, 4.3.2, and 5.4.1.
osv:CVE-2026-84375
Complete source record
{
"id": "6f23e09c65ddc63a26ff659fa42a16ea8838427ec6b70a6f74a9b7a21a9a2c10",
"url": "https://osv.dev/vulnerability/CVE-2026-84375",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources",
"summary": "js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 until 3.15.2, 4.3.2, and 5.4.1, maxTotalMergeKeys in lib/js-yaml/loader.js and lib/loader.js does not count empty mapping sources while processing the merge key <<. An attacker can alias a large sequence of empty mappings into many merge targets, causing O(N * K) processing while totalMergeKeys remains unchanged and the configured resource limit is never reached. A relatively small YAML document can therefore cause prolonged CPU consumption in applications that parse untrusted YAML, and merge processing is enabled by default on these release lines. In v3 & v4, merge is enabled by default so the severity score is higher. This issue is fixed in versions 3.15.2, 4.3.2, and 5.4.1.",
"evidence": "osv:CVE-2026-84375",
"products": [],
"severity": "high",
"structured": {
"id": "CVE-2026-84375",
"aliases": [
"CVE-2026-84375",
"GHSA-2883-xcg3-v3hh"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/nodeca/js-yaml",
"type": "GIT",
"events": [
{
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{
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{
"fixed": "3485bc06ff8a0251505f44a00414d90df2466639"
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{
"fixed": "6a8e05f9a485188ed730ac81e81ae221352ef480"
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{
"fixed": "d90b6612a5a84385bdcb556c44578eac76dc0f6b"
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"database_specific": {
"extracted_events": [
{
"range": [
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"introduced": "3.0.0"
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{
"fixed": "3.15.2"
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"source": "AFFECTED_FIELD",
"strategy": "StringRangeExpression"
},
{
"range": [
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"introduced": "4.0.0"
},
{
"fixed": "4.3.2"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StringRangeExpression"
},
{
"range": [
{
"introduced": "5.0.0"
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{
"fixed": "5.4.1"
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],
"source": "AFFECTED_FIELD",
"strategy": "StringRangeExpression"
},
{
"range": [
{
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"source": "REFERENCES_COMMIT"
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"source": "REFERENCES_COMMIT"
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"source": "REFERENCES_COMMIT"
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"range": [
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],
"source": "REFERENCES_TAG",
"original_tag": "3.15.2"
},
{
"range": [
{
"fixed": "79ca68d90f333fbe6d9e42827527e62636200191"
}
],
"source": "REFERENCES_TAG",
"original_tag": "4.3.2"
},
{
"range": [
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],
"source": "REFERENCES_TAG",
"original_tag": "5.4.1"
}
]
}
}
],
"versions": [
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"4.3.1",
"5.4.0",
"5.3.0",
"5.2.3",
"3.15.0",
"4.3.0",
"5.2.2",
"5.2.1",
"3.14.2",
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"3.11.0",
"3.10.0",
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"3.8.4",
"3.8.3",
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"3.7.0",
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"3.6.0",
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"3.5.3",
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"3.2.5",
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"3.2.3",
"3.2.2",
"3.2.1",
"3.2.0",
"3.1.0",
"3.0.2",
"3.0.1",
"3.0.0"
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-84375.json"
}
}
],
"modified": "2026-10-28T02:30:32.619677209Z",
"provider": "osv",
"references": [
"https://github.com/nodeca/js-yaml/releases/tag/3.15.2",
"https://github.com/nodeca/js-yaml/releases/tag/4.3.2",
"https://github.com/nodeca/js-yaml/releases/tag/5.4.1",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84375.json",
"https://github.com/nodeca/js-yaml/security/advisories/GHSA-2883-xcg3-v3hh",
"https://nvd.nist.gov/vuln/detail/CVE-2026-84375",
"https://github.com/nodeca/js-yaml/commit/3485bc06ff8a0251505f44a00414d90df2466639",
"https://github.com/nodeca/js-yaml/commit/6a8e05f9a485188ed730ac81e81ae221352ef480",
"https://github.com/nodeca/js-yaml/commit/d90b6612a5a84385bdcb556c44578eac76dc0f6b",
"https://github.com/nodeca/js-yaml/pull/797"
],
"provider_metadata": {
"cwe_ids": [
"CWE-400",
"CWE-407"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84375.json"
}
},
"related_cves": [
{
"value": "CVE-2026-84375",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 499581,
"published_at": "2026-09-01T21:43:13.617+00:00"
}