Vulnerability Description
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 from 7.24.1 up to 7.29.1 and from 8.0.0 up 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.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Nodejs | Undici | >= 7.24.1, < 7.29.1 |
Related Weaknesses (CWE)
References
- https://cna.openjsf.org/security-advisories.htmlThird Party Advisory
- https://github.com/nodejs/undici/security/advisories/GHSA-w293-vg96-wgc3MitigationVendor Advisory
FAQ
What is CVE-2026-84961?
CVE-2026-84961 is a vulnerability with a CVSS score of 7.4 (HIGH). 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-...
How severe is CVE-2026-84961?
CVE-2026-84961 has been rated HIGH with a CVSS base score of 7.4/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-84961?
Check the references section above for vendor advisories and patch information. Affected products include: Nodejs Undici.