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Fencer Vulns
high 7.5

CVE-2026-76169 json

fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers

published 2026-09-04 2 mo ago modified 2026-10-01 39 d ago also GHSA-p68q-wchp-6fh7 , EUVD-2026-70988

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 45%
public exploits
0
none known

Summary

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.

Patch / fix

  • npm fastify 5.12.2
  • fastify fastify 5.12.2

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-76169 updated cvss 7.5

fastify: fastify: Authentication bypass via malformed URLs

  • Red Hat Enterprise Linux AI (RHEL AI) 3 rhelai3/bootc-cuda-rhel9, rhelai3/bootc-rocm-rhel9, rhelai3/bootc-gaudi-rhel9, rhelai3/disk-image-cuda-rhel9
    affected: workaround, no fix available, no fix planned “Will not fix”
  • Red Hat OpenShift AI 2.25 rhoai/odh-dashboard-rhel9 1791853525, rhoai/odh-mod-arch-model-registry-rhel9 1791853432
    fixed: vendor fix RHSA-2026:87410
  • Red Hat OpenShift AI 3.4 rhoai/odh-dashboard-rhel9 1791861020, rhoai/odh-mod-arch-maas-rhel9 1791860708, rhoai/odh-mod-arch-automl-rhel9 1791861032, rhoai/odh-mod-arch-gen-ai-rhel9 1791861479, rhoai/odh-mod-arch-mlflow-rhel9 1791861383, rhoai/odh-mod-arch-autorag-rhel9 1791860994, +2 more
    fixed: vendor fix RHSA-2026:84734
  • Red Hat OpenShift AI 3.5 rhoai/odh-core-bff-rhel9 1791945789, rhoai/odh-dashboard-rhel9 1791945160, rhoai/odh-mod-arch-maas-rhel9 1791945249, rhoai/odh-mod-arch-automl-rhel9 1791945173, rhoai/odh-mod-arch-gen-ai-rhel9 1791944979, rhoai/odh-mod-arch-mlflow-rhel9 1791945636, +5 more
    fixed: vendor fix RHSA-2026:86891
  • Red Hat OpenShift Dev Spaces 3.31 devspaces/dashboard-rhel9 1791945540
    fixed: vendor fix RHSA-2026:90321
  • Red Hat OpenShift AI 2.25 rhoai/odh-rhel9-operator 1792570619, rhoai/odh-vllm-cpu-rhel9 1792018436, rhoai/odh-modelmesh-rhel9 1790881700, rhoai/odh-operator-bundle 1792571069, rhoai/odh-vllm-cuda-rhel9 1791358976, rhoai/odh-vllm-rocm-rhel9 1791282503, +64 more Red Hat OpenShift AI 3.4 rhoai/odh-cli-rhel9 1791509689, rhoai/rhai-cli-rhel9 1791509689, rhoai/odh-automl-rhel9 1791535789, rhoai/odh-mlflow-rhel9 1791865967, rhoai/odh-autorag-rhel9 1791557539, rhoai/odh-trainer-rhel9 1791869783, +92 more Red Hat OpenShift AI 3.5 rhoai/odh-cli-rhel9 1791945905, rhoai/rhai-cli-rhel9 1791945905, rhoai/odh-automl-rhel9 1791916705, rhoai/odh-mlflow-rhel9 1791947857, rhoai/odh-autorag-rhel9 1791903266, rhoai/odh-trainer-rhel9 1791952138, +102 more Red Hat OpenShift Dev Spaces 3.31 devspaces/udi-rhel9 1792708612, devspaces/code-rhel9 1792599388, devspaces/server-rhel9 1792775639, devspaces/openvsx-rhel9 1792494821, devspaces/traefik-rhel9 1792464177, devspaces/udi-base-rhel9 1792686842, +9 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.53% chance of exploitation in the next 30 days, higher than 45% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
npm fastify
>=4.0.0, <5.12.2
5.12.2

Affected products

  • fastify fastify

Classification

Weakness
  • CWE-288 Authentication Bypass Using an Alternate Path or Channel

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.