Summary
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 js-yaml dependency should be expressed as "^4.2.0" (instead of "4.2.x") so that dependent modules will not require yet another cfenv update the next time js-yaml needs a security fix (the last time was only a few months ago).
Published: March 03, 2026
Updated: June 18, 2026
Underscore.js is a utility-belt library for JavaScript. Prior to 1.13.8, the _.flatten and _.isEqual functions use recursion without a depth limit. Under very specific conditions, detailed below, an attacker could exploit this in a Denial of Service (DoS) attack by triggering a stack overflow. Untrusted input must be used to create a recursive datastructure, for example using JSON.parse, with no enforced depth limit. The datastructure thus created must be passed to _.flatten or _.isEqual. In the case of _.flatten, the vulnerability can only be exploited if it is possible for a remote client to prepare a datastructure that consists of arrays at all levels AND if no finite depth limit is passed as the second argument to _.flatten. In the case of _.isEqual, the vulnerability can only be exploited if there exists a code path in which two distinct datastructures that were submitted by the same remote client are compared using _.isEqual. For example, if a client submits data that are stored in a database, and the same client can later submit another datastructure that is then compared to the data that were saved in the database previously, OR if a client submits a single request, but its data are parsed twice, creating two non-identical but equivalent datastructures that are then compared. Exceptions originating from the call to _.flatten or _.isEqual, as a result of a stack overflow, are not being caught. This vulnerability is fixed in 1.13.8.
Likewise, the underscore dependency should be expressed as "^1.13.8" to avoid future issues.
js-yamldependency must be updated to address CVE-2026-53550.The
js-yamldependency should be expressed as "^4.2.0" (instead of "4.2.x") so that dependent modules will not require yet anothercfenvupdate the next timejs-yamlneeds a security fix (the last time was only a few months ago).underscoredependency must be updated to address CVE-2026-27601:Likewise, the
underscoredependency should be expressed as "^1.13.8" to avoid future issues.