CVE-2026-109383
7.4HighPublished 15 Oct 2026 · NVD status: Undergoing Analysis · AI triage by gemini-3.8-flash
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- None
- User interaction
- None
- Impact
- High impact on confidentiality, integrity
- Weakness
- CWE-295
Impact
A network adversary able to present an otherwise valid TLS certificate can bypass custom certificate validation or pinning logic to intercept or alter outbound traffic. This requires the attacker to position themselves as a TLS peer against an application that supplies a custom checkServerIdentity callback via undici's tls option.
Root cause
The Agent constructor runs its options through a JSON-based deep clone that silently drops function-valued properties, omitting custom checkServerIdentity verification callbacks before options reach the TLS layer.
Affected systems
undici 4.0.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1
CVSS v3.1 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Fix & remediation
Upgrade to undici 6.29.1, 7.30.1, or 8.12.2 or later. If patching cannot happen immediately, supply TLS options through the connect option instead of tls, or use requestTls and proxyTls for proxied routes.
$ npm install undici@latestAI-suggested. Run it in staging first and check it against the vendor advisory. Why?
NVD description
undici is an HTTP client library for Node.js. In versions 4.0.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, its Agent dispatcher passes its constructor options through a JSON-based deep clone before forwarding them to each per-origin pool, and because JSON cannot represent functions, a caller-supplied tls option containing a checkServerIdentity callback is silently dropped before it reaches the TLS layer. As a result, a TLS peer whose certificate a custom checkServerIdentity was written to reject, but which passes Node's default hostname and chain checks, is silently accepted. Because Agent is the default dispatcher behind request, fetch, and setGlobalDispatcher, this affects the path most applications use, and EnvHttpProxyAgent is affected on its direct and no-proxy routes as well, while only applications that pass a function-valued tls option such as a custom checkServerIdentity for certificate or public-key pinning are at risk. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, which preserve the tls option outside the JSON clone so custom verification callbacks are forwarded unchanged, and users should upgrade to one of those versions or later. As a workaround, pass the TLS options through connect instead of tls, or for proxied destinations use requestTls and proxyTls.