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Fencer Vulns
medium 4.8

CVE-2026-86818 json

fast-uri vulnerable to mailto header injection via percent-encoded field-name desynchronization

published 2026-09-15 55 d ago modified 2026-09-30 40 d ago also EUVD-2026-78403 , GHSA-jvvf-x445-j334

cvss
4.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 16%
public exploits
0
none known

Summary

fast-uri is a dependency-free RFC 3986 URI parser for Node.js, used by Fastify and ajv, that added a mailto scheme parser in version 4.1.3. In versions 4.1.3 and 4.1.4, the mailto parser compares each query field name to the reserved names to, subject, and body while the name is still percent-encoded, and decodes it only when storing it as a generic header, so a percent-encoded spelling of a reserved field name is not recognized as that field at parse time but is re-emitted as the literal field name when the parsed URI is serialized. An application that validates, logs, or displays the recipient list from the first parse and then serializes the URI and sends it can silently gain an attacker-chosen recipient, and the subject and body fields can be smuggled across the same roundtrip. The issue is fixed in fast-uri 4.1.5, and users should upgrade to 4.1.5 or later. As a workaround, do not act on a mailto URI that fast-uri has re-serialized without first decoding and re-validating its recipient, subject, and body fields.

Patch / fix

  • npm fast-uri 4.1.5
  • fast-uri fast-uri 4.1.5
  • node-ajv Debian 14 8.20.0~ds+~cs7.1.6-1

debian advisories DEBIAN-CVE-2026-86818

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-2026-86818 updated cvss 4.8

fast-uri: fast-uri: Mailto header injection via percent-encoded field-name desynchronization

  • Red Hat Satellite 6 satellite/iop-remediations-rhel9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Cost Management On Premise costmanagement/costmanagement-ui-rhel10 Red Hat Migration Toolkit for Applications 8 mta/mta-solution-server-rhel9 Red Hat Migration Toolkit for Containers rhmtc/openshift-migration-ui-rhel8 Red Hat Multicluster Engine for Kubernetes multicluster-engine/console-mce-rhel9 Red Hat Network Observability Operator network-observability/network-observability-console-plugin-rhel9, network-observability/network-observability-console-plugin-pf5-rhel9 Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-console-plugin-rhel9, openshift-lightspeed/lightspeed-agentic-console-rhel9, openshift-lightspeed/lightspeed-console-plugin-419-rhel9, openshift-lightspeed/lightspeed-console-plugin-pf5-rhel9
    +18 more products
    Red Hat OpenShift Pipelines openshift-pipelines/pipelines-hub-ui-rhel8, openshift-pipelines/pipelines-hub-ui-rhel9, openshift-pipelines/pipelines-console-plugin-rhel9, openshift-pipelines/pipelines-console-plugin-pf5-rhel9 Red Hat OpenShift Serverless openshift-serverless-1/kn-eventing-integrations-log-sink-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-s3-sink-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-sns-sink-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-sqs-sink-rhel9, openshift-serverless-1/kn-eventing-integrations-timer-source-rhel9, openshift-serverless-1/kn-eventing-integrations-aws-s3-source-rhel9, +3 more Red Hat Advanced Cluster Management for Kubernetes 2 rhacm2/console-rhel9 Red Hat AMQ Broker 7 amq-broker-bin.zip 7.14.1.CR3, amq-broker-maven-repository.zip 7.14.1.CR3 Red Hat Ansible Automation Platform 2 automation-platform-ui 2.6.13-1.el9ap, automation-gateway 2.5.20260824-1.el8ap, ansible-automation-platform-24/lightspeed-rhel8, ansible-automation-platform-25/lightspeed-rhel8, ansible-automation-platform-26/lightspeed-rhel9, ansible-automation-platform-27/mcp-server-rhel9, +1 more Red Hat build of Apache Camel - HawtIO 4 rhaf-hawtio-maven-repository.zip 4.4.0.GA Red Hat build of Apicurio Registry 3 apicurio/apicurio-registry-ui-rhel8 Red Hat Build of Podman Desktop rh-podman-desktop.git 1.1.0 Red Hat Data Grid 8 redhat-datagrid-maven-repository.zip 8.6.1.CR1 Red Hat Developer Hub 1 rhdh/rhdh-hub-rhel9, rhdh/red-hat-developer-hub-backstage-plugin-orchestrator, rhdh/red-hat-developer-hub-backstage-plugin-lightspeed-backend, rhdh/red-hat-developer-hub-backstage-plugin-orchestrator-backend, rhdh/red-hat-developer-hub-backstage-plugin-orchestrator-form-widgets, rhdh/red-hat-developer-hub-backstage-plugin-orchestrator-backend-module-loki, +1 more Red Hat Directory Server 11 389-ds-base 1.4.3.34-18.module+el8dsrv+24812+0acb1821 Red Hat Directory Server 12 389-ds-base 2.2.7-18.module+el9dsrv+24814+6d9b6eb5 Red Hat Discovery 2 discovery/discovery-ui-rhel9 Red Hat Edge Manager 1 rhem/flightctl-ui-rhel9, rhem/flightctl-ui-rhel10, rhem/flightctl-ui-ocp-rhel9, rhem/flightctl-ui-ocp-rhel10 Red Hat Enterprise Linux 8 dotnet, dotnet-host, dotnet-sdk-8.0, dotnet-hostfxr-8.0, dotnet-runtime-8.0, dotnet-sdk-dbg-8.0, +10 more Red Hat Enterprise Linux 9 sgx-mpa, tdx-qgs, sgx-libs, sgx-pccs, sgx-common, dotnet-host, +17 more Red Hat Enterprise Linux 10 grafana 12.4.3-2.el10, linux-sgx 2.26-7.el10, dotnet8.0 8.0.130-2.el10, grafana-pcp 6.1.0-1.el10, cockpit-image-builder 110-1.el10 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
    not affected: vulnerable code not present
  • Red Hat Hardened Images jaeger 2.20.0-0.8.hum1, dotnet8.0 8.0.130-2.el10, grafana13.1 13.1.3-0.8.hum1, grafana13.2 13.2.1-0.3.hum1, grafana12.4 12.4.10-0.2.hum1, prometheus3.13 3.13.3-0.1.hum1
    not affected: component not present
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-mlflow-rhel9, rhoai/odh-core-bff-rhel9, rhoai/odh-dashboard-rhel9, rhoai/odh-mod-arch-maas-rhel9, rhoai/odh-feature-server-rhel9, rhoai/odh-mod-arch-automl-rhel9, +8 more Red Hat OpenShift Container Platform 4 openshift4/ose-console-rhel9, openshift4/ose-monitoring-plugin-rhel9, openshift4/nmstate-console-plugin-rhel9 Red Hat OpenShift Container Platform 5 openshift5/ose-console-rhel9, openshift5/ose-monitoring-plugin-rhel9, openshift5/nmstate-console-plugin-rhel9 Red Hat Openshift Data Foundation 4 odf4/mcg-core-rhel9, odf4/odf-console-rhel9, odf4/ocs-client-console-rhel9, odf4/odf-multicluster-console-rhel9 Red Hat OpenShift Dev Spaces devspaces/code-rhel9, devspaces/openvsx-rhel9, devspaces/dashboard-rhel9 Red Hat Quay 3 quay/quay-rhel8, quay/quay-rhel9
    +3 more products
    Red Hat Satellite 6 nodejs-webpack 5.109.2-1.el9sat, satellite/iop-advisor-frontend-rhel9, satellite/iop-vulnerability-frontend-rhel9, satellite/iop-host-inventory-frontend-rhel9, nodejs-mini-css-extract-plugin 2.10.2-2.el9sat, nodejs-compression-webpack-plugin 10.0.0-3.el9sat Red Hat Secrets Management Console for Red Hat OpenShift external-secrets-management/console-plugin-rhel9 Red Hat Self-service automation portal 2 ansible-automation-platform/automation-portal, ansible-automation-platform/bootc-automation-portal-rhel9
    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
partial
Assessed
55 d ago

Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
GitHub 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
npm fast-uri
>=4.1.3, <4.1.5
4.1.5

Affected products

  • fast-uri fast-uri

Classification

Weakness
  • CWE-172 Improper Encoding or Decoding of Data
  • CWE-436 Interpretation Conflict

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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.