PYSEC-2026-1630

### Impact In mitmweb 11.1.0 and below, a malicious client can use mitmweb's proxy server (bound to `*:8080` by default) to access mitmweb's internal API (bound to `127.0.0.1:8081` by default). In other words, while the client cannot access the API directly (good), they can access the API through the proxy (bad). An attacker may be able to escalate this [SSRF](https://en.wikipedia.org/wiki/Server-side_request_forgery)-style access to remote code execution.

The mitmproxy and mitmdump tools are unaffected. Only mitmweb is affected. The `block_global` option, which is enabled by default, blocks connections originating from publicly-routable IP addresses in the proxy. The attacker needs to be in the same local network.

### Patches

The vulnerability has been fixed in mitmproxy 11.1.2 and above.

### Acknowledgements

We thank Stefan Grönke (@gronke) for reporting this vulnerability as part of a security audit by [Radically Open Security](https://www.radicallyopensecurity.com/). This audit was supported by the [NGI0 Entrust fund](https://nlnet.nl/entrust/) established by [NLnet](https://nlnet.nl/).

### Timeline

- **2025-01-14**: Received initial report. - **2025-01-14**: Verified report and confirmed receipt. - **2025-01-19**: Shared patch with researcher. - **2025-02-04**: Received final confirmation that patch is working. - **2025-02-05**: Published patched release and advisory.