Axios is a promise-based HTTP client for the browser and Node.js. From 1.16.1 until 1.20.0, the RFC 2397 regular expression allows slash characters on both sides of the media-type separator. An application passes an attacker-controlled malformed data URL containing many slash characters and no comma. the JavaScript regular-expression engine explores many separator placements before rejecting the URL. Synchronous excessive backtracking can block the Node.js event loop and cause denial of service. The affected identifiers are fromDataURI, DATA_URL_PATTERN, data:. This issue is fixed in version 1.20.0.

Affected: npm: axios

## Summary

Axios for Node.js parses `data:` URLs in `lib/helpers/fromDataURI.js`. The current RFC-2397 parser uses a regular expression whose media type groups allow `/` inside both sides of the `type/subtype` match. A malformed `data:` URL containing many slashes and no comma forces the JavaScript regex engine to try many possible placements for the separator before failing.

Applications are affected when they pass untrusted URL strings to axios and do not reject or constrain `data:` URLs before axios parses them.

## Impact

An attacker can make the Node.js event loop spend significant synchronous CPU time parsing a single malformed URL. In a server that accepts a URL from an HTTP request and calls `axios.get(url)`, this can block unrelated requests and health checks until parsing completes.

The issue is availability-only. It does not disclose data or modify requests.

## Affected Functionality

Affected:

- Node.js HTTP adapter data URL handling. - `axios.get()` or equivalent calls where `config.url` has the `data:` protocol.

Not affected:

- Browser fetch/XHR URL handling. - Node requests where the application rejects `data:` URLs before calling axios. - Older checked `0.x` data URL parser shape unless separately proven vulnerable.

## Technical Details

`lib/helpers/fromDataURI.js` contains:

```js const DATA_URL_PATTERN = /^([^,;]+\/[^,;]+)?((?:;[^,;=]+=[^,;]+)*)(;base64)?,([\s\S]*)$/; ```

The `[^,;]+` groups include `/`, so a long string of slashes without a comm…

Affected: Ubuntu:Pro:20.04:LTS: node-axios, Ubuntu:Pro:22.04:LTS: node-axios, Ubuntu:Pro:24.04:LTS: node-axios, Ubuntu:Pro:26.04:LTS: node-axios

Axios is a promise-based HTTP client for the browser and Node.js. From 1.16.1 until 1.20.0, the RFC 2397 regular expression allows slash characters on both sides of the media-type separator. An application passes an attacker-controlled malformed data URL containing many slash characters and no comma. the JavaScript regular-expression engine explores many separator placements before rejecting the URL. Synchronous excessive backtracking can block the Node.js event loop and cause denial of service. The affected identifiers are fromDataURI, DATA_URL_PATTERN, data:. This issue is fixed in version 1.20.0.