Quick answers
- Is This vulnerability exploited in the wild?
- No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
- How severe is This vulnerability?
- Low severity, with a CVSS score of 3.1, published 29 March 2026.
- Which products and versions are affected?
- handlebars (npm) SEMVER:introduced=4.6.0,fixed=4.7.9.
- Is there a fix for This vulnerability?
- Yes. handlebars (npm): upgrade to 4.7.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is This vulnerability attacked?
- It is attacked over the network.
- Am I affected?
- Check whether you run handlebars (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- handlebars (npm): upgrade to 4.7.9 or later
npm install handlebars@4.7.9
Technical details
The vulnerability is a prototype method access control gap in lib/handlebars/internal/proto-access.js. The blocklist blocks constructor, __defineGetter__, __defineSetter__, and __lookupGetter__ but omits __lookupSetter__, creating an asymmetric security boundary. When the non-default runtime option allowProtoMethodsByDefault: true is set, any prototype method not in the blocklist is permitted by default. An attacker can reference __lookupSetter__ through untrusted template input to bypass access controls. This only affects applications that explicitly enable allowProtoMethodsByDefault: true; the default configuration is not affected. The vulnerability was fixed in version 4.7.9.
Affected products
- Handlebars Handlebars.js 4.6.0 through 4.7.8
Timeline
- 2026-03-29: disclosed: GHSA-7rx3-28cr-v5wh published
- 2026-03-26: patched: Fixed in version 4.7.9