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Full vulnerability report · 2026
CVE-2026-16732High confidence

fastify vulnerable to X-Forwarded-* spoofing under trustProxy hop-count

fastify · fastify

6.1MediumCVSS 3.1
Recommended action
Scheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-16732 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityfastify: fastify: Request spoofing via numeric trustProxy configuration
16 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • rhelai3/bootc-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3
  • rhelai3/bootc-gaudi-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3
  • rhelai3/bootc-rocm-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3
  • rhelai3/disk-image-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3
  • rhoai/odh-core-bff-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
  • rhoai/odh-dashboard-operator-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
  • rhoai/odh-dashboard-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
  • rhoai/odh-mod-arch-agent-ops-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
  • rhoai/odh-mod-arch-automl-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
  • rhoai/odh-mod-arch-autorag-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
  • rhoai/odh-mod-arch-eval-hub-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
  • rhoai/odh-mod-arch-gen-ai-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
Summary
A flaw was found in fastify. When configured with a numeric `trustProxy` value, an attacker who can directly access the Fastify origin, bypassing the front-facing proxy, can spoof forwarded request fields. This vulnerability allows for host injection in generated URLs, bypasses HTTPS enforcement, and can lead to secure-cookie and Cross-Site Request Forgery (CSRF) origin bypasses, as well as host-based routing and cache poisoning.
Remediation
Fix deferred
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-61222

No EUVD known-exploited evidence

fastify vulnerable to X-Forwarded-* spoofing under trustProxy hop-count

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
6.1 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionScheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
01

What, why and how

fastify is a fast and low overhead web framework for Node.js. Impact: the fix for CVE-2026-3635 added a guard on the forwarded-header reads used to derive the request host, protocol, hostname, ip, and ips values, checking the connecting address. That guard closes the IP, CIDR, and custom-function forms of trustProxy correctly, because those forms compile to predicates that inspect the connecting address. The hop-count form, where trustProxy is set to a number, compiles to a predicate that structurally ignores the address, so the guard is always satisfied for any hop count of one or more. Applications configured with a numeric trustProxy value, such as trustProxy set to 1 for a single reverse proxy, remain vulnerable: an attacker who can reach the Fastify origin directly, bypassing the front-facing proxy, can spoof the forwarded request fields exactly as in the unpatched version. The impact class matches the parent CVE-2026-3635, including host injection in generated URLs, HTTPS-enforcement bypass, secure-cookie and CSRF-origin bypass, and host-based routing and cache poisoning. Affected versions are fastify from 5.8.3 up to but not including 5.12.1. Patches: patched in fastify 5.12.1, where the numeric form of trustProxy is disabled at runtime and removed from the TypeScript type union. Workarounds: migrate to an IP, CIDR, or custom-function trustProxy value that validates the connecting address, and ensure the Fastify origin is only reachable through the trusted proxy chain.

What

fastify is a fast and low overhead web framework for Node.js. Impact: the fix for CVE-2026-3635 added a guard on the forwarded-header reads used to derive the request host, protocol, hostname, ip, and ips values, checking the connecting address. That guard closes the IP, CIDR, and custom-function forms of trustProxy correctly, because those forms compile to predicates that inspect the connecting address. The hop-count form, where trustProxy is set to a number, compiles to a predicate that structurally ignores the address, so the guard is always satisfied for any hop count of one or more. Applications configured with a numeric trustProxy value, such as trustProxy set to 1 for a single reverse proxy, remain vulnerable: an attacker who can reach the Fastify origin directly, bypassing the front-facing proxy, can spoof the forwarded request fields exactly as in the unpatched version. The impact class matches the parent CVE-2026-3635, including host injection in generated URLs, HTTPS-enforcement bypass, secure-cookie and CSRF-origin bypass, and host-based routing and cache poisoning. Affected versions are fastify from 5.8.3 up to but not including 5.12.1. Patches: patched in fastify 5.12.1, where the numeric form of trustProxy is disabled at runtime and removed from the TypeScript type union. Workarounds: migrate to an IP, CIDR, or custom-function trustProxy value that validates the connecting address, and ensure the Fastify origin is only reachable through the trusted proxy chain.

Why

The product has two different sources of the same data or information, but it uses the source that has less support for verification, is less trusted, or is less resistant to attack.

How

An attacker operating through an adjacent network may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

fastify is a fast and low overhead web framework for Node.js. Impact: the fix for CVE-2026-3635 added a guard on the forwarded-header reads used to derive the request host, protocol, hostname, ip, and ips values, checking the connecting address. That guard closes the IP, CIDR, and custom-function forms of trustProxy correctly, because those forms compile to predicates that inspect the connecting address. The hop-count form, where trustProxy is set to a number, compiles to a predicate that structurally ignores the address, so the guard is always satisfied for any hop count of one or more. Applications configured with a numeric trustProxy value, such as trustProxy set to 1 for a single reverse proxy, remain vulnerable: an attacker who can reach the Fastify origin directly, bypassing the front-facing proxy, can spoof the forwarded request fields exactly as in the unpatched version. The impact class matches the parent CVE-2026-3635, including host injection in generated URLs, HTTPS-enforcement bypass, secure-cookie and CSRF-origin bypass, and host-based routing and cache poisoning. Affected versions are fastify from 5.8.3 up to but not including 5.12.1. Patches: patched in fastify 5.12.1, where the numeric form of trustProxy is disabled at runtime and removed from the TypeScript type union. Workarounds: migrate to an IP, CIDR, or custom-function trustProxy value that validates the connecting address, and ensure the Fastify origin is only reachable through the trusted proxy chain.

Why

The product has two different sources of the same data or information, but it uses the source that has less support for verification, is less trusted, or is less resistant to attack.

How

An attacker operating through an adjacent network may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
an adjacent network → Use of Less Trusted Source → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Adjacent
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Changed: exploitation can affect a different security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-348 ↗

CWE-348: Use of Less Trusted Source. The product has two different sources of the same data or information, but it uses the source that has less support for verification, is less trusted, or is less resistant to attack.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVAdjacentAttack vector: The attacker must be on an adjacent or logically close network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SChangedScope: The attack can affect a component governed by a different security authority.CHighConfidentiality impact: A successful attack can cause a major loss.INoneIntegrity impact: No direct loss is represented by this metric.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
UnauthenticatedCWE-348
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-61222Official EUVD mapping

fastify vulnerable to X-Forwarded-* spoofing under trustProxy hop-count

Official EUVD record
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
rhelai3/bootc-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; rhelai3/bootc-gaudi-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; rhelai3/bootc-rocm-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; rhelai3/disk-image-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; rhoai/odh-core-bff-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-dashboard-operator-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-dashboard-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-mod-arch-agent-ops-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-mod-arch-automl-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-mod-arch-autorag-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-mod-arch-eval-hub-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-mod-arch-gen-ai-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-mod-arch-maas-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-mod-arch-mlflow-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-mod-arch-model-registry-rhel9 as a component of Red Hat OpenShift AI (RHOAI); devspaces/dashboard-rhel9 as a component of Red Hat OpenShift Dev Spaces
Fixed
5.12.1
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
A mitigation or workaround reference is available from the source linked below; validate it against the affected product and version.
04

Evidence and provenance

Published 18 Aug 2026 · Last source change 19 Aug 2026, 13:16 UTC · CWE-348 · Use of Less Trusted Source

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-23
European sourceENISA EUVD · EUVD-2026-61222
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →
  1. Vendor guidanceAuthoritative vendor guidance changed from authoritative remediation link to authoritative remediation link · mitigation.
    Before
    authoritative remediation link
    After
    authoritative remediation link · mitigation
    ce714d77-add3-4f53-aff5-83d477b104bb ↗
  2. Catalogue recordCVE added to the BlackTree catalogue.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-61222↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-16732 · cve.blacktree.nl