CVE-2026-6734: undici vulnerable to cross-origin request routing via SOCKS5 proxy pool reuse

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-17 · updated 2026-09-10
Weakness: CWE-346

Description

Impact: 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.

Affected products

undici: from 7.23.0 before 7.28.0; from 8.0.0 before 8.2.0 — fixed in 7.28.0, 8.2.0

How to fix

Upgrade to a fixed version: undici 7.28.0, 8.2.0. Check the vendor advisory for mitigations.

References

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