High [CVE-2026-6734] Information disclosure and data integrity issues due to incorrect Socks5ProxyAgent connection routing

When using Socks5ProxyAgent, undici reuses a single connection pool across different origins without verifying that the pool's origin matches the requested origin. All requests are dispatched through the pool connected to the first origin, regardless of the intended destination.

This causes cross-origin request routing: credentials and request data intended for origin B are sent to origin A, responses from the wrong origin are trusted, and HTTPS requests may be silently downgraded to HTTP. Impacted users are applications that use Socks5ProxyAgent (directly or via setGlobalDispatcher) and make requests to more than one origin.

This was introduced in undici 7.23.0 via PR #4385 and affects all versions through 8.1.0. Patches: Upgrade to undici v7.26.0 or v8.2.0.

Workarounds: Use a separate Socks5ProxyAgent instance per origin, or avoid using Socks5ProxyAgent with multiple origins. Consequently, responses from unintended origins may be trusted, and secure HTTPS connections could be silently downgraded to unencrypted HTTP, resulting in information disclosure and data integrity issues.

This is rated as an Important security flaw. The `undici` library, when configured with `Socks5ProxyAgent` to handle requests for multiple origins, incorrectly reuses connection pools.