Executive brief
Undici, a popular HTTP client for Node.js, contains a flaw in how it handles secure proxy connections. When configured to use a SOCKS5 proxy, the library may mistakenly send sensitive data, such as login credentials or private request details, to the wrong website. This could lead to data theft, the acceptance of fraudulent data from incorrect sources, or the accidental bypass of encryption.
Technical details
A vulnerability exists in undici's Socks5ProxyAgent where the library reuses a single connection pool across different origins without verifying that the pool's origin matches the requested destination. Consequently, all requests are dispatched through the connection pool established for the first origin visited. An attacker can exploit this to intercept credentials and request data intended for one origin by receiving them at another, or cause the client to trust responses from an incorrect source. Additionally, this flaw can lead to silent HTTPS-to-HTTP downgrades. The issue was introduced in version 7.23.0 and is fixed in versions 7.28.0 and 8.2.0.
Affected products
- Node.js undici >= 7.23.0, < 7.28.0; >= 8.0.0, < 8.2.0
Timeline
- 2026-06-17: disclosed
- 2026-06-17: advisory
- 2026-06-17: patched