# CVE-2026-47099: telejson XSS — Fixed in 6.0.0

📦 npm

Not in CISA KEV

# 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

Also known as[GHSA-ccgf-5rwj-j3hv](/vulnerability/GHSA-ccgf-5rwj-j3hv)

Published

May 20, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

## 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

[via FIRST.org ↗](https://www.first.org/epss/)

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs30th percentile — riskier than 30% of all scored CVEsHighest risk

0.00%0.29%0.59%0.88%0.0%0.4%Jun 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.first.org/epss/).

## Real-World Exposure

1 pkg affected

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.

74other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

`telejson`npm

3.6Mdownloads / week

## 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](https://github.com/storybookjs/telejson/blob/v5.3.3/src/index.ts#L293-L299)):

```
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](https://github.com/storybookjs/telejson/blob/v6.0.0/src/index.ts#L340-L346)):

```
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

1 total 1 fixed

Ecosystem

Package

Vulnerable range

Fix

📦npm

`telejson` 

all versions

6.0.0`npm install telejson@6.0.0`

## Detection & mitigation playbook

Open-source dependency

1.  ### Detect
    
    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.
    
2.  ### 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.
    
3.  ### Workarounds
    
    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
    

## Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Workaround published by Red Hat

> Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Source: [Red Hat security advisory for CVE-2026-47099](https://access.redhat.com/security/cve/cve-2026-47099) (CC BY 4.0)

## Frequently Asked Questions

\## 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 proces

O3 Security · Impact-Aware SCA

### Is CVE-2026-47099 in your dependencies?

Find it across npm, including transitive dependencies.

[Scan my dependencies](/book-demo) [How O3 SCA works](/impact-aware-sca)