CVE-2026-53550
js-yaml: Quadratic-complexity DoS in merge key handling via repeated aliases
Description
js-yaml is a JavaScript YAML parser and dumper. Prior to 4.2.0 and 3.15.0, a crafted YAML document can trigger algorithmic CPU exhaustion in js-yaml merge-key processing (<<) by repeating the same alias many times in a merge sequence. This causes quadratic parse-time behavior relative to input size and can block a Node.js worker/event loop for seconds with a relatively small payload (tens of KB), resulting in denial of service. The issue is in merge handling inside lib/loader.js. This vulnerability is fixed in 4.2.0 and 3.15.0.
INFO
Published Date :
June 22, 2026, 4:16 p.m.
Last Modified :
July 9, 2026, 8:33 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update js-yaml to version 4.2.0 or later.
- Ensure merge-key processing is handled safely.
- Monitor resource usage for YAML parsing.
Public PoC/Exploit Available at Github
CVE-2026-53550 has a 2 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-53550.
| URL | Resource |
|---|---|
| https://github.com/nodeca/js-yaml/security/advisories/GHSA-h67p-54hq-rp68 | Exploit Mitigation Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-53550 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-53550
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
None
Node.js SDK that abstracts the calls to Companies House public APIs
Makefile JavaScript TypeScript
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-53550 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-53550 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Modified Analysis by [email protected]
Jul. 09, 2026
Action Type Old Value New Value Changed CPE Configuration OR *cpe:2.3:a:nodeca:js-yaml:*:*:*:*:*:node.js:*:* versions up to (excluding) 4.2.0 OR *cpe:2.3:a:nodeca:js-yaml:*:*:*:*:*:node.js:*:* versions up to (excluding) 3.15.0 *cpe:2.3:a:nodeca:js-yaml:*:*:*:*:*:node.js:*:* versions from (including) 4.0.0 up to (excluding) 4.2.0 -
CVE Modified by [email protected]
Jun. 29, 2026
Action Type Old Value New Value Changed Affected [{'vendor': 'nodeca', 'product': 'js-yaml', 'versions': [{'status': 'affected', 'version': '< 4.2.0'}]}] [{'vendor': 'nodeca', 'product': 'js-yaml', 'versions': [{'status': 'affected', 'version': '>= 4.0.0, < 4.2.0'}, {'status': 'affected', 'version': '< 3.15.0'}]}] Changed Description js-yaml is a JavaScript YAML parser and dumper. Prior to 4.2.0, a crafted YAML document can trigger algorithmic CPU exhaustion in js-yaml merge-key processing (<<) by repeating the same alias many times in a merge sequence. This causes quadratic parse-time behavior relative to input size and can block a Node.js worker/event loop for seconds with a relatively small payload (tens of KB), resulting in denial of service. The issue is in merge handling inside lib/loader.js. This vulnerability is fixed in 4.2.0. js-yaml is a JavaScript YAML parser and dumper. Prior to 4.2.0 and 3.15.0, a crafted YAML document can trigger algorithmic CPU exhaustion in js-yaml merge-key processing (<<) by repeating the same alias many times in a merge sequence. This causes quadratic parse-time behavior relative to input size and can block a Node.js worker/event loop for seconds with a relatively small payload (tens of KB), resulting in denial of service. The issue is in merge handling inside lib/loader.js. This vulnerability is fixed in 4.2.0 and 3.15.0. -
Initial Analysis by [email protected]
Jun. 26, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:nodeca:js-yaml:*:*:*:*:*:node.js:*:* versions up to (excluding) 4.2.0 Added Reference Type GitHub, Inc.: https://github.com/nodeca/js-yaml/security/advisories/GHSA-h67p-54hq-rp68 Types: Exploit, Mitigation, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 23, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-53550', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-06-23T16:05:40.611324Z'} -
New CVE Received by [email protected]
Jun. 22, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'nodeca', 'product': 'js-yaml', 'versions': [{'status': 'affected', 'version': '< 4.2.0'}]}] Added Description js-yaml is a JavaScript YAML parser and dumper. Prior to 4.2.0, a crafted YAML document can trigger algorithmic CPU exhaustion in js-yaml merge-key processing (<<) by repeating the same alias many times in a merge sequence. This causes quadratic parse-time behavior relative to input size and can block a Node.js worker/event loop for seconds with a relatively small payload (tens of KB), resulting in denial of service. The issue is in merge handling inside lib/loader.js. This vulnerability is fixed in 4.2.0. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Added CWE CWE-407 Added Reference https://github.com/nodeca/js-yaml/security/advisories/GHSA-h67p-54hq-rp68