GHSA-442j-39wm-28r2
LOWHandlebars.js has a Property Access Validation Bypass in container.lookup
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
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 | 4.7.9 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for handlebars. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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 pinpoints whether GHSA-442j-39wm-28r2 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
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 detects GHSA-442j-39wm-28r2 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.