GHSA-442j-39wm-28r2 is a low-severity (CVSS 3.7) vulnerability in handlebars. A fix is available for handlebars — see the affected versions and patch details below.
Handlebars.js has a Property Access Validation Bypass in container.lookup
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
handlebarsnpmDescription
Summary
In lib/handlebars/runtime.js, the container.lookup() function uses container.lookupProperty() as a gate check to enforce prototype-access controls, but then discards the validated result and performs a second, unguarded property access (depths[i][name]). This Time-of-Check Time-of-Use (TOCTOU) pattern means the security check and the actual read are decoupled, and the raw access bypasses any sanitization that lookupProperty may perform.
Only relevant when the compat compile option is enabled ({compat: true}), which activates depthedLookup in lib/handlebars/compiler/javascript-compiler.js.
Description
The vulnerable code in lib/handlebars/runtime.js (lines 137–144):
lookup: function (depths, name) {
const len = depths.length;
for (let i = 0; i < len; i++) {
let result = depths[i] && container.lookupProperty(depths[i], name);
if (result != null) {
return depths[i][name]; // BUG: should be `return result;`
}
}
},
container.lookupProperty() (lines 119–136) enforces hasOwnProperty checks and resultIsAllowed() prototype-access controls. However, container.lookup() only uses lookupProperty as a boolean gate — if the gate passes (result != null), it then performs an independent, raw depths[i][name] access that circumvents any transformation or wrapped value that lookupProperty may have returned.
Workarounds
- Avoid enabling
{ compat: true }when rendering templates that include untrusted data. - Ensure context data objects are plain JSON (no Proxies, no getter-based accessor properties).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | handlebars | ≥ 4.0.0&&< 4.7.9 | 4.7.9npm install handlebars@4.7.9 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for handlebars, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update handlebars to 4.7.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-442j-39wm-28r2 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-442j-39wm-28r2 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-442j-39wm-28r2. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-442j-39wm-28r2 in your dependencies?
O3 Security finds GHSA-442j-39wm-28r2 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.