Versions of handlebars prior to 4.0.0 are affected by a cross-site scripting vulnerability when attributes in handlebar templates are not quoted.

Proof of Concept

Template:
<a href={{foo}}/>

Input:
{ 'foo' : 'test.com onload=alert(1)'}

Rendered result:
<a href=test.com onload=alert(1)/>

Recommendation

Update to version 4.0.0 or later.
Alternatively, ensure that all attributes in handlebars templates are encapsulated with quotes.

References

• https://nvd.nist.gov/vuln/detail/CVE-2015-8861
• handlebars-lang/handlebars.js#1083
• https://blog.srcclr.com/handlebars_vulnerability_research_findings/
• GHSA-9prh-257w-9277
• https://www.npmjs.com/advisories/61
• https://www.sourceclear.com/blog/handlebars_vulnerability_research_findings/
• https://www.tenable.com/security/tns-2016-18
• http://www.openwall.com/lists/oss-security/2016/04/20/11
• http://www.securityfocus.com/bid/96434