Axios' HTTP adapter-streamed uploads bypass maxBodyLength when maxRedirects: 0

Summary

For stream request bodies, maxBodyLength is bypassed when maxRedirects is set to 0 (native http/https transport path). Oversized streamed uploads are sent fully even when the caller sets strict body limits.

Details

Relevant flow in lib/adapters/http.js:

• 556-564: maxBodyLength check applies only to buffered/non-stream data.
• 681-682: maxRedirects === 0 selects native http/https transport.
• 694-699: options.maxBodyLength is set, but native transport does not enforce it.
• 925-945: stream is piped directly to socket (data.pipe(req)) with no Axios byte counting.

This creates a path-specific bypass for streamed uploads.

PoC

Environment:

• Axios main at commit f7a4ee2
• Node v24.2.0

Steps:

1. Start an HTTP server that counts uploaded bytes and returns {received}.
2. Send a 2 MiB Readable stream with:
   • adapter: 'http'
   • maxBodyLength: 1024
   • maxRedirects: 0

Observed:

• Request succeeds; server reports received: 2097152.

Control checks:

• Same stream with default/nonzero redirects: rejected with ERR_FR_MAX_BODY_LENGTH_EXCEEDED.
• Buffered body with maxRedirects: 0: rejected with ERR_BAD_REQUEST.

Impact

Type: DoS / uncontrolled upstream upload / resource exhaustion. Impacted: Node.js services using streamed request bodies with maxBodyLength expecting hard enforcement, especially when following Axios guidance to use maxRedirects: 0 for streams.