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Fencer Vulns
high 8.1

CVE-2026-84504 json

fastify vulnerable to request body replacement via an async validation result collision

published 2026-09-04 2 mo ago modified 2026-10-01 39 d ago also GHSA-667r-xxjv-c9mm , EUVD-2026-70984

cvss
8.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 37%
public exploits
0
none known

Summary

fastify versions before 5.12.2 treat the object resolved by a successful Ajv async validator as the value result protocol used by custom validator compilers. If a request that passes its route schema contains a property named value at the root, fastify replaces the entire request body with that property's value before the handler runs, so the handler receives a different object than the one that satisfied the schema. An authenticated low-privilege caller can use this to make nested data replace the validated body and trigger an operation the route schema did not authorize, leading to unauthorized state changes and data disclosure. 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-2026-84504 updated cvss 8.1

fastify: fastify: Unauthorized state changes and data disclosure via request body replacement

  • 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
no
Technical impact
total
Assessed
2 mo ago

Exploit prediction

0.43% chance of exploitation in the next 30 days, higher than 37% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
GitHub 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Affected packages

ecosystem package affected fixed in
npm fastify
<5.12.2
5.12.2

Affected products

  • fastify fastify

Classification

Weakness
  • CWE-20 Improper Input Validation

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.