CVE-2026-59868: js-yaml: YAML merge-key chains can force quadratic CPU consumption
Vulnerability summary
CVE-2026-59868 is a high (CVSS 7.5) Inefficient Algorithmic Complexity vulnerability in nodeca js-yaml. EPSS estimates a 0.64% chance of exploitation in the next 30 days, higher than 50.9% of scored vulnerabilities. 1 public exploit is recorded.
Not severe (CVSS 5.3, network access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 8Timeline
- 08-07-2026PublishedVulnerability first disclosed.
- 09-07-2026Last modifiedVulnerability information updated.
Description
js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 before 5.2.0, when merge keys are enabled, js-yaml can spend quadratic CPU time parsing a document whose size grows only linearly when a chain of mappings uses merge keys where each mapping merges the previous one. This issue is fixed in version 5.2.0.
CVSS metrics
4 scores · 4 sources · 1 version- CVE.orgCNA5.3MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:LDiffers
- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- OSV · NpmEcosystem advisory · calculated5.3MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:LDiffers
EPSS trend
Probability
0.64%
Chance of exploitation in the next 30 days
Percentile
51%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.64% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
1 foundJs Yaml
Maturity: poc
Weaknesses
CWE · root cause- CWE-407Inefficient Algorithmic ComplexityAn algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
- CWE-770Allocation of Resources Without Limits or ThrottlingThe product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
Affected systems
Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Nodeca1 product
- js-yaml≥ 5.0.0, < 5.2.0
Npm1 product
- js-yaml≥ 5.0.0, < 5.2.0
Ubuntu1 product
- node-js-yamlAll versions (No fix recorded)
3 vendors · 3 products
References
7 links- github.com/nodeca/js-yaml/security/advisories/GHSA-g796-fgmg-93mvX Refsource CONFIRMREPORTWEBExploitVendor Advisory
- github.com/nodeca/js-yamlPACKAGE