Arbitrary remote code execution within `wrangler dev` Workers sandbox

Impact

The V8 inspector intentionally allows arbitrary code execution within the Workers sandbox for debugging. wrangler dev would previously start an inspector server listening on all network interfaces. This would allow an attacker on the local network to connect to the inspector and run arbitrary code. Additionally, the inspector server did not validate Origin/Host headers, granting an attacker that can trick any user on the local network into opening a malicious website the ability to run code. If wrangler dev --remote was being used, an attacker could access production resources if they were bound to the worker.

Patches

This issue was fixed in wrangler@3.19.0 and wrangler@2.20.2. Whilst wrangler dev's inspector server listens on local interfaces by default as of wrangler@3.16.0, an SSRF vulnerability in miniflare allowed access from the local network until wrangler@3.18.0. wrangler@3.19.0 and wrangler@2.20.2 introduced validation for the Origin/Host headers.

Workarounds

Unfortunately, Wrangler doesn't provide any configuration for which host that inspector server should listen on. Please upgrade to at least wrangler@3.16.0, and configure Wrangler to listen on local interfaces instead with wrangler dev --ip 127.0.0.1 to prevent SSRF. This removes the local network as an attack vector, but does not prevent an attack from visiting a malicious website.

References

• https://github.com/cloudflare/workers-sdk/issues/4430
• https://github.com/cloudflare/workers-sdk/pull/4437
• https://github.com/cloudflare/workers-sdk/pull/4535
• https://github.com/cloudflare/workers-sdk/pull/4550