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CVE-2026-59870— js-yaml quadratic-complexity denial of service via YAML11_SCHEMA !!omap parsing

Quick assessment

Affected
nodeca js-yaml
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Nodeca JS-YAML是Nodeca个人开发者开源的一个JavaScript YAML解析器和转储器。 Nodeca js-yaml 5.2.1之前版本存在资源管理错误漏洞，该漏洞源于src/tag/sequence/omap.ts中!!omap标签的YAML11_SCHEMA支持使用omapTag.addItem()进行线性重复键扫描，导致解析特制有序映射文档时CPU消耗呈O(n²)增长，容易受到资源消耗攻击。以下版本受到影响：5.0.0版本至5.2.1之前版本。

CVSS 5.3 · Medium EPSS 0.64% · P49

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProduct Version RangeStatus
nodeca js-yaml >= 5.0.0, < 5.2.1 affected
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I. Basic Information for CVE-2026-59870

Vulnerability Information
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Vulnerability Title
js-yaml quadratic-complexity denial of service via YAML11_SCHEMA !!omap parsing
Source: CVE Program / CVE List V5
Vulnerability Description
js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 before 5.2.1, YAML11_SCHEMA support for the !!omap tag in src/tag/sequence/omap.ts uses omapTag.addItem() to perform a linear duplicate-key scan on every insertion, causing O(n^2) CPU consumption when yaml.load() parses a crafted ordered-map document. This issue is fixed in version 5.2.1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
算法复杂性
Source: CVE Program / CVE List V5
Vulnerability Title
Nodeca js-yaml 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Nodeca JS-YAML是Nodeca个人开发者开源的一个JavaScript YAML解析器和转储器。 Nodeca js-yaml 5.2.1之前版本存在资源管理错误漏洞，该漏洞源于src/tag/sequence/omap.ts中!!omap标签的YAML11_SCHEMA支持使用omapTag.addItem()进行线性重复键扫描，导致解析特制有序映射文档时CPU消耗呈O(n²)增长，容易受到资源消耗攻击。以下版本受到影响：5.0.0版本至5.2.1之前版本。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
nodeca js-yaml >= 5.0.0, < 5.2.1 -

II. Public POCs for CVE-2026-59870

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Reproduced successfully in a real sandbox · Below is the actual recording of building the environment and exploiting the vulnerability.
Success marker: VULNERABLE: CVE-2026-59870 RESULT:VULNERABLE 5.2.0 n=20000 elapsed=6238ms n=10000 elapsed=799ms ratio=7.81 (quadratic growth in !!omap parsing)
Reproduction recording is a Pro+ exclusive
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claude_code · 3961 chars
GitHub 复现环境（可 clone 直接跑）
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III. Intelligence Information for CVE-2026-59870

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Patches & Fixes for CVE-2026-59870 (1)

Vendor Advisories for CVE-2026-59870 (1)

Same Patch Batch · nodeca · 2026-07-08 · 3 CVEs total

CVE-2026-59869 7.5 HIGH js-yaml: YAML merge-key chains can force quadratic CPU consumption
CVE-2026-59868 5.3 MEDIUM js-yaml: YAML merge-key chains can force quadratic CPU consumption

IV. Related Vulnerabilities

Same product: js-yaml
Same vendor: nodeca
Same weakness: CWE-407

V. Comments for CVE-2026-59870

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