GHSA-ccgf-5rwj-j3hv
MEDIUMGHSA-ccgf-5rwj-j3hv is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in telejson. O3 Security confirms whether GHSA-ccgf-5rwj-j3hv is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
TeleJSON: DOM XSS via unsanitised constructor name in `new Function()`
Blast Radius
telejsonReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
Summary
telejson versions prior to 6.0.0 (released 2022) are vulnerable to DOM-based Cross-Site Scripting (XSS) through unsafe deserialisation. Attacker-controlled input from the _constructor-name_ property in parsed JSON is passed directly to new Function() without sanitisation, allowing arbitrary JavaScript execution.
Affected versions
| Package | Affected | Fixed |
|---|---|---|
| telejson | < 6.0.0 | >= 6.0.0 |
Details
telejson's parse() function uses a custom reviver to reconstruct JavaScript objects from serialised JSON. When processing objects with a _constructor-name_ property, the reviver passes the constructor name directly to new Function() to recreate the object's prototype.
In versions prior to 6.0.0, this constructor name is not sanitised. An attacker who can deliver a crafted JSON payload to telejson.parse() (for example, via postMessage in applications that use telejson for cross-frame communication) can inject arbitrary JavaScript into the new Function() call.
Vulnerable code (src/index.ts, lines 293-299 at v5.3.3):
if (isObject<ValueContainer>(value) && value['_constructor-name_']) {
const name = value['_constructor-name_'];
if (name !== 'Object') {
const Fn = new Function(`return function ${name}(){}`)();
Object.setPrototypeOf(value, new Fn());
}
Fixed code (src/index.ts, lines 340-346 at v6.0.0):
if (isObject<ValueContainer>(value) && value['_constructor-name_'] && options.allowFunction) {
const name = value['_constructor-name_'];
if (name !== 'Object') {
const Fn = new Function(`return function ${name.replace(/[\W_]+/g, '')}(){}`)();
Object.setPrototypeOf(value, new Fn());
}
The fix introduces two mitigations: a character allowlist via regex that strips non-word characters before they reach new Function(), and gating the entire code path behind the allowFunction option.
Impact
An attacker can execute arbitrary JavaScript in the context of the application using the vulnerable telejson version. Depending on the application, this could enable session hijacking, credential theft, or arbitrary DOM manipulation.
Remediation
Upgrade to telejson >= 6.0.0.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | telejson | all versions | 6.0.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for telejson. 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 telejson to 6.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-ccgf-5rwj-j3hv 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-ccgf-5rwj-j3hv 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-ccgf-5rwj-j3hv. 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-ccgf-5rwj-j3hv in your dependencies?
O3 detects GHSA-ccgf-5rwj-j3hv across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.