Improper Certificate Validation Affecting org.webjars.npm:undici package, versions [7.27.1,]
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published6 Sept 2026
- disclosed4 Sept 2026
- creditJoshua Rogers
Introduced: 4 Sep 2026
NewCVE-2026-84961 (opens in a new tab)How to fix?
A fix was pushed into the master branch but not yet published.
Overview
org.webjars.npm:undici is an An HTTP/1.1 client, written from scratch for Node.js
Affected versions of this package are vulnerable to Improper Certificate Validation in the BalancedPool class, which deep-clones its connect and tls options with JSON.parse(JSON.stringify(...)) and thereby silently drops any function-valued callbacks, such as a custom checkServerIdentity or connector, before they reach the TLS layer. An attacker can present a server certificate that the caller's custom checkServerIdentity was written to reject and still have it accepted, as long as it passes Node's default hostname and chain checks, because the discarded check never runs. This affects only BalancedPool configured with function-valued connect or tls options, and not Client, Pool, Agent, or RoundRobinPool.
Workaround
This vulnerability can be avoided by using Client, Pool, or Agent instead of BalancedPool for connections that rely on a custom checkServerIdentity or connector, so the callback is not stripped before reaching the TLS layer.