CVE-2026-75975

About vulnerability

Impact

fast-uri does not validate the complete RFC 3986 grammar for bracketed IPv6 literals, so a malformed literal with invalid trailing text is silently truncated to a different valid IPv6 address with no error reported. For example, normalize('http://[::not-valid]/private') returns http://[::]/private, and [fc00::not-hex] and [fe80::not-hex] collapse to [fc00::] and [fe80::]. An application that normalizes an untrusted URL before an outbound request, redirect, or host-policy check can be routed to a local or private address such as loopback (::1), unique-local, or link-local. Because parse().error is unset for these inputs, checking it does not protect the consumer.

Patches

Upgrade to fast-uri 2.4.5, 3.1.6, or 4.1.3. Malformed IPv6 literals are now rejected with a host error instead of being normalized to a valid address.

Workarounds

Reject untrusted URLs whose host is a bracketed IPv6 literal before passing them to fast-uri, or route outbound requests against an explicit allowlist of addresses rather than trusting the normalized host.

Affected product:

AngularJS , Fastify , Node.js , React , Vue , ajv , ajv-compiler , ajv-draft-04 , ajv-errors , ajv-formats , ajv-keywords , api-extractor-model , babel-loader , cache-loader , css-loader , css-minimizer-webpack-plugin , devkit , esbuild-loader , extract-css-chunks-webpack-plugin , fast-json-stringify , fast-json-stringify-compiler , fast-uri , file-loader , fork-ts-checker-webpack-plugin , friendly-errors-webpack-plugin , hard-source-webpack-plugin , html-webpack-plugin , light-my-request , mini-css-extract-plugin , minimizer-webpack-plugin , nuxt , optimize-css-assets-webpack-plugin , postcss-loader , rushstack , schema-utils , style-resources-loader , table , thread-loader , time-fix-plugin , ts-command-line , tsdoc , url-loader , webpack , webpack-dev-middleware , webpack-dev-server , webpackbar , worker-loader

Affected packages:

fastify @ 4.29.1 (+463 more)