The package handlebars before 4.7.7 are vulnerable to Prototype Pollution when selecting certain compiling options to compile templates coming from an untrusted source.

The package handlebars before 4.7.7 are vulnerable to Remote Code Execution (RCE) when selecting certain compiling options to compile templates coming from an untrusted source.

Handlebars before 3.0.8 and 4.x before 4.5.3 is vulnerable to Arbitrary Code Execution. The lookup helper fails to properly validate templates, allowing attackers to submit templates that execute arbitrary JavaScript. This can be used to run arbitrary code on a server processing Handlebars templates or in a victim's browser (effectively serving as XSS).

Handlebars before 4.4.5 allows Regular Expression Denial of Service (ReDoS) because of eager matching. The parser may be forced into an endless loop while processing crafted templates. This may allow attackers to exhaust system resources.