CVE-2026-47099 — telejson
CVE-2026-47099 is a Cross-site Scripting (XSS) vulnerability in telejson. A fix is available for telejson — see the affected versions and patch details below.
TeleJSON < 6.0.0 DOM-based XSS via parse() Function
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-47099.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
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.
telejsonnpmDescription
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 | 6.0.0npm install telejson@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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update telejson to 6.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-47099 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 CVE-2026-47099 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-47099. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-47099 in your dependencies?
O3 Security finds CVE-2026-47099 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.