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Improper Certificate Validation in undici

CVE-2026-84961

  • undici
High
9.1/10

Summary

undici's `BalancedPool` constructor passes its entire options object through an internal deep-clone that serializes and reparses the value as JSON. Because JSON cannot represent functions, any function-valued TLS option, such as a caller-supplied `checkServerIdentity` callback or a custom connector inside the connect option, is silently discarded before it reaches the TLS layer. As a result a peer whose certificate the application's custom `checkServerIdentity` was written to reject, but which still passes Node's default hostname and chain checks, is accepted when reached through `BalancedPool`. The Client, Pool, and Agent dispatchers are not affected because they extract the connect and tls options before cloning. This affects undici versions 7.24.1 prior to 7.29.1 and 8.0.0 prior to 8.10.2, and only when the application supplies a function-valued connect or tls option to BalancedPool. Users should upgrade to undici 7.29.1 or 8.10.2.

  • LOW
  • NETWORK
  • HIGH
  • UNCHANGED
  • NONE
  • NONE
  • HIGH
  • NONE

CWE-295 - Improper Certificate Validation

The authenticity component of a web system stems from the ability to validate “Digital certificates”, which (i) establish trust between two or more entities sharing data over a network; (ii) ensure data at rest and transit is secure from unauthorized access; and (iii) check the identity of the actors that interact with the system. An application with absent or ineffective certificate validation mechanisms allows malicious users, impersonating trusted hosts, to manipulate the communication path between the client and the host, resulting in unauthorized access to data and to the application’s internal environment, and potentially enabling man-in-the-middle attacks.

References

Advisory Timeline

  • Published