nodeca js-yaml up to 5.2.1 Parser src/parser/parser.ts readFlowCollection infinite loop

Summaryinfo

A vulnerability identified as problematic has been detected in nodeca js-yaml up to 5.2.1. Affected by this vulnerability is the function readFlowCollection of the file src/parser/parser.ts of the component Parser. The manipulation leads to infinite loop. This vulnerability is documented as CVE-2026-73643. The attack can be initiated remotely. There is not any exploit available.

Detailsinfo

A vulnerability was found in nodeca js-yaml up to 5.2.1 and classified as problematic. This issue affects the function readFlowCollection of the file src/parser/parser.ts of the component Parser. The manipulation with an unknown input leads to a infinite loop vulnerability. Using CWE to declare the problem leads to CWE-835. The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. Impacted is availability. The summary by CVE is:

js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 until 5.2.2, parsing a small YAML document can take exponential time when an application calls load() or loadAll() on untrusted input. In src/parser/parser.ts, readFlowCollection uses restoreState and calls parseNode a second time when a flow-sequence entry is recognized as a key: value pair. If the key is a nested flow sequence of the same shape, every level is parsed twice, causing O(2^n) work and allowing an input under 200 bytes to keep one CPU busy for minutes, block the Node.js event loop, and stall the process. No anchors, aliases, merges, tags, or nondefault options are required. This issue is fixed in version 5.2.2.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-73643 since 08/13/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 5.2.2 eliminates this vulnerability.

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Productinfo

Vendor

• nodeca

Name

• js-yaml

Version

• 5.2.0
• 5.2.1

Website

• Product: https://github.com/nodeca/js-yaml/

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