Arbitrary Code Execution in handlebars

2020-09-04T14:57:38
ID GHSA-2CF5-4W76-R9QV
Type github
Reporter GitHub Advisory Database
Modified 2020-09-04T14:57:38

Description

Versions of handlebars prior to 3.0.8 or 4.5.2 are vulnerable to Arbitrary Code Execution. The package's lookup helper fails to properly validate templates, allowing attackers to submit templates that execute arbitrary JavaScript in the system. It can be used to run arbitrary code in a server processing Handlebars templates or on a victim's browser (effectively serving as Cross-Site Scripting).

The following template can be used to demonstrate the vulnerability:
{{#with "constructor"}} {{#with split as |a|}} {{pop (push "alert('Vulnerable Handlebars JS');")}} {{#with (concat (lookup join (slice 0 1)))}} {{#each (slice 2 3)}} {{#with (apply 0 a)}} {{.}} {{/with}} {{/each}} {{/with}} {{/with}} {{/with}}

Recommendation

Upgrade to version 3.0.8, 4.5.2 or later.