fastify versions >= 4.0.0 and before 5.12.2 can route a malformed URL sent under one plugin prefix to the custom not-found handler of a different sibling plugin, and invoke it without the preHandler hook declared for that handler. The internal not-found router for encapsulated handlers dispatches malformed paths through a single shared handler pointer before URL decoding, ignoring the prefix and skipping the selected handler's normal lifecycle. An unauthenticated attacker can therefore reach an authentication-protected private fallback through an unrelated public prefix and read its full response, bypassing the authentication hook and breaking prefix encapsulation. Users should upgrade to fastify 5.12.2 or later.

A flaw was found in fastify. Malformed URLs can be routed to a custom not-found handler of a different plugin, bypassing the intended security checks. This allows an unauthenticated attacker to access and read the full response of an authentication-protected private fallback, leading to information disclosure and an authentication bypass.

This is an Important flaw in fastify that allows an unauthenticated attacker to bypass authentication hooks. By sending a specially crafted malformed URL, an attacker can access private fallback handlers and read their responses, thereby circumventing intended access controls in Red Hat OpenShift AI and Red Hat OpenShift Dev Spaces deployments. Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability. Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/bootc-cuda-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/bootc-gaudi-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/bootc-rocm-rhel9 Red Hat Enterprise Linux AI (RHEL AI) 3 Affected rhelai3/disk-image-cuda-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-core-bff-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-dashboard-operator-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-dashboard-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-mod-arch-agent-ops-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-mod-arch-automl-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-mod-arch-autorag-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-mod-arch-eval-hub-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-mod-arch-gen-ai-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-mod-arch-maas-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-mod-arch-mlflow-rhel9 Red Hat OpenShift AI (RHOAI) Affected rhoai/odh-mod-arch-model-registry-rhel9 Red Hat OpenShift Dev Spaces Affected devspaces/dashboard-rhel9 https://www.cve.org/CVERecord?id=CVE-2026-76169 https://nvd.nist.gov/vuln/detail/CVE-2026-76169 https://cna.openjsf.org/security-advisories.html https://github.com/fastify/fastify/security/advisories/GHSA-p68q-wchp-6fh7